The aftereffects of a typical geomagnetic storm (the duration 24 h, in the frequency range 0–5 Hz) on the activity of glycosidase (maltase, amylolytic activity) in the intestine of a 4-month juvenile roach Rutilus rutilus (L.) have been studied. Embryos were exposed to geomagnetic storm 72 h later after fertilization. The amylolytic activity was determined by Nelson method and the maltase activity by the glucose-oxidase method. The level of glycosidase activity in juvenile roach under the impact of geomagnetic storm was significantly lower than that in controls. Temperature characteristics of glycosidase in fish of the experimental and the control groups are similar. Temperature optimum of amylolytic activity was observed at 40 єC, the temperature optimum of maltase was found at 60 єC. The Eact values of maltase at the temperature 0-30 °C are similar in both groups of yearlings. The Eact values of amylolytic activity at feeding temperature 10-20 °C were significantly lower (the efficiency of the process is higher) than at lower temperatures in both groups of yearlings