Seasonal dynamics of cephalothorax length (CL), caudal setae length (CSL) and II exopodites of 5th swimming legs length (LL) on females and males of 5th-4th copepodid stages of Epischura baicalensis in Southern Baikal natural population ones was investigated. On the adult females CL and LL was assessed, on the adult males – CL and CSL. It was shown, that max values of CL in summer, min – in begin (spring) or in end (winter) year was
observed. In spring and summer in population dominate crustacean with high CSL, in autumn and winter – low or medium ones. High values of LL characterized in spring-summer and low in autumn-winter. Different problems of Epischura biology for solution which received data might be value was discussed.