The Athens 2004 gold medallist came out on top again in a hard-fought final bout with Xu Li of China, the youngest woman in the event at 18, who won silver. Colombian Jackeline Renteria and Tonya Verbeek of Canada won bronze medals.
Yoshida wept as the Japanese anthem was played.
"I cried because I killed myself preparing for these Olympics ... I cried because I was really happy," she said.
The Japan-China clash in one of the Games' few single combat, full-contact sports was anticipated with relish by home fans packing the China Agricultural University gym, who rattled the rafters with chants of "China, China".
"I was fighting not to be overwhelmed by the Chinese fans shouting," said Yoshida.
Xu had thrilled the crowd with fearless and powerful assaults in qualifying bouts. But in the final, her inexperience told. The match stopped at 43 seconds into the second, two-minute period, with a surprised Xu neatly pinned to the mat.
"For six months I have been thinking about this and working very hard to make this happen," said the 25-year-old Japanese, who executed two back somersaults across the centre mat in celebration as Japanese fans cheered.
Yoshida was held in awe by her opponents in the qualifying bouts. Ide-Theres Nerell of Sweden said she felt "empty" when she realised she was drawn against the formidable Japanese.
Nerell's coach said Yoshida "doesn't show anything, and then something happens".
She has won the last five world championship titles and now successfully defended her gold from Athens 2004, where women's wrestling was introduced to the Olympics.
But the Japanese champ got a wake-up call in January when her amazing 119-match winning streak was broken by American Marcie van Dusen and was anything but complacent.
"I've really been carrying around with me in my head what happened in January," she said. "I realised if I stayed the way I was I would not win in Beijing."
Yoshida said she plans to compete in the 2012 Olympics in London, where she could meet a more experienced Xu.
For the moment, the Chinese teenager acknowledged that she still had lots to learn.
"I felt a little disappointed to lose the gold medal, but the silver is good enough for an 18-year-old, since I am too young and I am not as good as Yoshida," Xu said.
"She defeated me in the Asian championship and she has more experience and skills than me. I will learn from this loss in my future training ... I want to defeat Yoshida," she said.
Huynh, 27, defeated Japanese two-times world champion Chiharu Icho, who took the silver in wrestling's lightest weight class. The score was 3-1.
Her parents were Chinese and settled in British Columbia, where she was born, after fleeing Saigon, now Ho Chi Minh City, said Huynh.
"It's very special to them to be here and see such an accomplishment and to see me reach my dream. And right in front of their eyes," said Huynh.
"I was the first in the family to be born in Canada. My parents are both very hard-working."
Icho made no excuses for her loss to the Canadian. "She was stronger physically and technically. Stronger in all respects," said the 26-year-old Japanese competitor.
Irini Merleni of Ukraine and Mariya Stadnik of Azerbaijan won bronze medals.
"Winning the bronze this time was even harder than winning the gold (at the Athens Olympics in 2004), even though I have been three-times world champion," said Merleni.
Canada's Tonya Vebeek later won bronze in the 55 kg category to give the country two medals from women's wrestling.
Age: 27 (date of birth: Nov 16, 1980)
Place of birth: Hazelton, Canada
Silver medallist, 2001 World Championships, women's 46kg
Bronze medallist, 2005 World Championships, women's 48kg
Bronze medallist, 2000 World Championships, women's 46kg
Huynh was a gold medal winner at the 2005 World Student Games in Izmir, Turkey. She enjoys reading, watching films and making necklaces and earrings.
Age: 25 (date of birth: Oct 5, 1982)
Place of birth: Mie, Japan
Five gold medals at World Championships (2002, 2003, 2005,
2006 and 2007), women's 55 kg
Three gold medals at Asian Championships (2005, 2007, 2008), women's 55kg
Previous Olympic result:
Gold medallist, 2004 Olympics, women's 55 kg
Yoshida started wrestling at the age of three. Her father was a national wrestling champion in Japan. She carried her country's flag at the opening ceremony of the 2006 Asian Games in Doha, Qatar. She enjoys singing karaoke songs.