Usoyan, 75, known as "Grandpa Hassan" and "Grandpa Khassan," was shot Wednesday as he left a restaurant.
The assailant, who escaped, fired six shots, only one of which hit Usoyan. Two struck and seriously injured a woman passerby, who was hospitalized, the Russian news service RIA Novosti reported.
The target of a previous assassination attempt in 2010, Usoyan died on the way to a hospital, the Russian website Pravda said.
Beginning in 2007 Usoyan was involved in a gang war with Georgian mobster Teriel Oniani, Pravda said.