Abstract: The change in behavior of basalt fiber-reinforced plastic (BFRP) after being held in a climatic chamber at 60 ºС and 100 % humidity for 2 months was investigated. Mechanical properties (strength, ultimate deformation, elastic modulus) were measured by the longitudinal bending technique; glass transition temperature was determined by TMA as per GOST 32618.2-2014; and the variation of the surface condition was evaluated by a special procedure of digital conversion of specimen surface micrographs into a greyshade distribution histogram. The mechanical behavior and glass transition of the specimens after climatic ageing were found to increase. This is explained by the plasticization effect and post-curing of the binder at elevated humidity and temperature. The findings are on a par with the literature data. The correlation was found between the surface condition variation and behavior variation of the BFRP specimens.