World champion Guo maintained China's domination of the event, which stretches to five consecutive Olympic titles following wins by Gao Min in 1988 and 1992 and Fu Mingxia in 1996 and 2000.
Guo, silver medallist in 2000, led a Chinese one-two, compiling a total of 633.15 points from her five-semi-final and five final dives to win from 18-year-old Wu Minxia, who scored 612.00.
Guo, 22, and Wu won the Athens synchronised three-metre springboard event.
Yulia Pakhalina of Russia, the 1998 world champion and 2003 silver medallist, dropped from silver to bronze on the last dive and finished with 610.62 points, having led through the qualifying rounds.
"I was not nervous or stressed during the competition because I knew I could do well," Guo said. "I am amazed about the gold medal. I have been training for this since I was five years old."
Wu said she was surprised at her high marks. "I did not expect to get such a high score. I'm very happy with the silver medal. I wasn't very nervous. I felt relaxed, so I did fine."
Guo, world champion in 2001 and 2003, seized the lead with her first dive of the final and picked up one perfect 10 score for each of her second and fourth dives.
Her marks were in the 80s in the second, third and fourth rounds in each of which she was the highest scorer.
Going into the last round, her lead over Pakhalina was a massive 37.38 points and it mattered little that her last dive was not so good.
Wu, world bronze medallist last year behind Guo and Pakhalina, enjoyed an excellent duel with the 26-year-old Russian European champion for second place and just snapped up the silver with her last dive, a slender 1.38 points ahead in an aggregate of more than 600 points.
"Something happened to me, my mind was blocked so I could not get the silver medal. Deep inside I am happy with the bronze. Were I to get the silver I would always think to myself 'why not the gold?'," Pakhalina said.
"I want to congratulate the Chinese girls, they did a great job today, great diving." She said the bronze completed her Olympic set following three-metre synchronised gold in Sydney and silver in Athens.
"I've got all three of them and I'm really happy," she said.
Russia's Vera Ilyina, silver medallist with Pakhalina behind Guo and Wu in the synchronised three-metre event, finished fourth on 589.11 but was never really in the medal hunt.