MMA Fighter Sergio Da Silva just pled not guilty to robbing a NYC bank over the summer ... TMZ Sports has learned.
Officials say Silva -- who fought at Bellator 180 -- busted into a CitiBank in Queens on August 24th claiming to have a gun, and threatening to shoot whoever didn't cooperate.
Cops say Silva got away with around $50K in cash.
Silva, who was present in the NYC court, plead not guilty to both charges.