The illegal use of formalin for quality control purposes is a widespread practice in today’s fish industry. Therefore, the present study was undertaken to assess the quality characteristics of formalin treated (5% formalin for 30 min) mrigel carp, Cirrhinus mrigala, Hamilton, stored on ice. The formalin detected was 12.19 ±0.814 μg g-1 for freshly treated samples and 8.10 ± 0.068 μg g-1 for treated samples stored on ice. In the control fish, the formalin concentration was almost negligible. The assessment of the organoleptic characteristics of the treated fish revealed that the gills had blackened, the eyes had become whitish and opaque, the muscles had lost tenderness, and the fish had stiffened. The quality assessment score of the control batch was significantly higher than that of the treated batch. The microbes in the fish were still lower than the amount specified for fish spoilage. Lipid hydrolysis in the treated fish was much higher than that of control, especially when storage time increased. High levels of trichloroacetic acid (TCA) soluble protein in the treated fish, as compared to that of the control fish, were observed throughout the storage period. Considering the low organoleptic status and poor nutritional quality, formalin treatment in the fish industry is not recommended even though the formalin content and the microbiological counts were still below permissible limits.