The purpose of this study is to investigate the discriminability of two different assimilation types, the Uncategorized-Categorized (UC) and the Uncategorized-Uncategorized assimilation (UU) (Best and Tyler, 2007), as reflected in the discrimination accuracy and reaction times towards non-native contrasts by Russian speakers. The discriminability of these assimilation types varies in the literature. To this purpose, the same Russian speakers who evaluated Greek consonantal contrasts as UC and UU types in an assimilation test of a previous study completed an AXB discrimination test in this study to detect the discriminability of these assimilation types. The findings demonstrated that most of the UU non-overlapping (UU-N) types, and specifically those with focalized-focalized responses, were more accurately discriminated and had faster RTs than the UC non-overlapping (UC-N) type. However, one UU-N type with clustered-clustered responses did not differ in terms of discrimination accuracy and reaction times with the UC-N type. It is suggested that despite having the same overlapping parameters (non-overlapping), UU types might be more discriminable than UC types with respect to consonants. Also, similarity of uncategorized phones with other assimilated phones (e.g., focalized, clustered, dispersed) might shape the UC-UU type relationship. Finally, it is assumed that the discriminability of UC-UU types might be consonant-specific.