Abstract We performed NH3 (J, K) = (1, 1), (2, 2), and (3, 3) mapping observations toward the Galactic massive star-forming region Sh 2-255 and Sh 2-257 using the Nobeyama 45 m telescope as a part of the KAGONMA (KAgoshima Galactic Object survey with the Nobeyama 45 metre telescope by Mapping in Ammonia lines) project. NH3 (1, 1) has an intensity peak at the cluster S255 N, is distributed over 3 pc × 2 pc, and is located between two H ii regions. The kinetic temperature derived from the NH3 (2, 2)/(1, 1) ratio was ∼35 K near the massive cluster S255 IR. These clusters also show emission with a large line width of ∼3–4 km s−1. Based on the reported data, we suggest that NH3 gas in these regions is affected by stellar feedback from embedded youn stellar object (YSO) clusters in S255 IR and S255 N. We also detected NH3 (1, 1) emission in a region west of the main gas clump at the location of a concentration of Class II YSOs adjacent to the H ii regions Sh 2-254. The presence of Class II YSOs implies ∼2 Myr of star formation, younger than Sh 2-254 (∼5 Myr), thus we suggest that star formation in the western region could be influenced by the older H ii region Sh 2-254.