Selective logging is the most widespread habitat disturbance in tropical forests. Primary forest set‐asides along riparian zones are mandated in many countries and a key question is whether these riparian reserves provide biodiversity conservation benefits. We characterise butterfly communities in fixed‐width riparian reserves of 30 m on each bank along narrow streams (<10 m) paired with interior logged forest transects, and in primary forests within a selective logging concession in the south‐western Brazilian Amazon. We found that primary forest species richness was more similar to riparian reserves than to paired interior logged forest points, whereas abundance remained higher in both riparian reserves and interior logged points, likely due to the intrusion of canopy‐dwelling species in disturbed habitats, as previously reported in the literature. Butterfly assemblages within riparian reserves were more similar to unlogged primary forests than interior logged points, and canopy height in riparian reserves was associated with increased assemblage similarity to primary forest points. Changes in abundance relative to primary forest were of a larger magnitude in interior logged points than in riparian reserves within logged forests, highlighting the role of riparian reserves in maintaining primary forest‐like communities. We found no particular primary forest butterfly clades to be more sensitive to changes in abundance than other clades. Synthesis and applications. Mandatory conservation set‐asides around streams or rivers (riparian buffers) have an important role in protecting the abundance and composition of primary forest butterfly assemblages within selective logging concessions in tropical rainforests. This study highlights the need to assess the conservation value of protecting unlogged riparian forest strips in other taxa to inform policy.