Krayzie Bone -- Bone Thugs Rapper Pleads NOT GUILTY to DUI

Bone Thugs-n-Harmony rapper Krayzie Bone insists he wasn't driving drunk when he was arrested over the summer, pleading "not guilty" to DUI today ... TMZ has learned.

As we first reported, Krayzie was arrested in late July on suspicion of DUI ... after cops pulled him over in L.A. during a routine traffic stop.

According to police, the rapper bombed his field sobriety test and later blew over .10 on the breathalyzer. The legal limit in California is .08.