Three rally organizers were arrested Saturday at a park in Russia's second city, and five others were detained at a later rally attempt near the landmark Smolny complex, Russian news agencies reported.
Only six people showed up for the second rally, and the three arrested at the first attempt were the only participants.
Although homosexuality was decriminalized after the fall of the Soviet Union, disdain for gays remains strong in Russia. Some rally attempts provoke violence by opponents.
St. Petersburg passed a law in February calling for fines of up to 500,000 rubles ($15,000) for spreading "homosexual propaganda."