Abstract: Biology of parthenogenetic females of Ceriodaphnia quadrangula(O.F.Muller)wasstudied under laboratory conditions at 25±1℃,Scenedesmus obliquus(Turp.)Kutz wasused as food for the animals during the experiments. The mean body -length of neonatesof C. quadrangula was 0.40mm and that of the first adult instar 0.96mm,A maximumlength of 1.45mm was attained.The growth in body─length(lt,in mm)in relation to age(t,in day)can be described as lt=1.43-e-0.268tThe mean longevity was found to be 22.73(17.10─25.00)days for 3 preadult and 13adult instars.Sexual maturity was reached in 3.91 days.40(19─47)young from 3 broods wereobtained in 7 days.The mean number of young per brood was 18.5(4.8─23.6).The totaloffspring production by one adult reached 222.1 during its life─span. The maximum re-production period occurred during the 6th adult instar. At this age,the animals were11.05 days old,and had a body length of 1.375mm.In a population originated from 10 individuals,the population growth curve of C. quadrangula was shown to be logistic and may be expressed as y=2220/1+e6.239-0.572t in which y denotes total number of individuals and t, days.The innate capacity for increase(rm)was 0.540 per female per day,the net repro-duction rate(Ro)was 147.360 per generation, the mean length of a generation(T)was9.246 days, and the finite rate ofincrease(λ)was 1.716 per female per day.