The effects of plasma etching on the evolution of surface roughness of GaN and AlN were discussed. The etch-induced roughness was analyzed using atomic force microscopy. The surface roughness was correlated to etch rate for both GaN and AlN. It was observed that the induced roughness remained comparable to the as-grown value provided etching was carried out below rates 400 (GaN) and 90nm/min (AlN). The cutoff etch rates and spatial-frequency dependence of the power spectral density (PSD) were also interpreted.