In the spring of 1905 Piatnitsky attended the 3rd Congress of the RSDLP in London. He returned to Russia later in that same year, going to Odessa in the Ukraine, where he worked as a Bolshevik organizer primarily among the tobacco workers there. Piatnitsky was an active participant in the Revolution of 1905, helping to organize a general strike in Odessa. Unsurprisingly, this activity again drew the scrutiny of the secret police and in January 1906 Piatnitsky was arrested again by the Okhrana.