In order to elucidate the biotoxicity of the urease inhibitor hydroquinone to the nitrogen-fixing cyanobacterium, Alinostoc sp. YYLX235, which was isolated from an acidified rice paddy field, the effects of hydroquinone (0.0, 2.5, 5.0, 10.0 mg/L) on the growth, photosynthesis, nitrogen fixing enzyme activity, antioxidant enzyme activity and oxidative damage characteristics of Alinostoc sp. YYLX235 were investigated on 2, 6 d. The results of concentration gradient toxicology tests showed that 2.5 mg/L hydroquinone had stimulating effects on the growth and phycobilin protein of Aliinostoc sp YYLX235 at the 2 d, but the stimulatory effect shifted to an inhibitory effect as the treatment time increased. Hydroquinone showed no significant effects on the contents of chlorophyll a and carotenoids in the cells of Aliinostoc sp. YYLX235. The electron transfer efficiency of photosystem Ⅱ(PSⅡ) of Aliinostoc sp. YYLX235 was sensitive to hydroquinone stress. The electron donating side of PS Ⅱ was severely damaged by hydroquinone, the maximum quantum yield of primary photochemistry of 5.0 mg/L hydroquinone treatment at 2 d was only 79.1% of that of the control. The activity of catalase(CAT) in the cells of Aliinostoc sp. YYLX235 was promoted by hydroquinone. The CAT activity of 10.0 mg/L hydroquinone treatment was 9.96 times that of the control at 6 d，while no oxidative damage on lipids was observed under hydroquinone stress. The activity of nitrogen fixation of Aliinostoc sp. YYLX235 was significantly inhibited by hydroquinone.