Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is one of the main threats to food security and farmers' livelihoods worldwide. For developing an effective management against this pest, improving the rearing technique and basic information on its biology is required. Therefore, this study was designed to assess the cohort rearing on each developmental stage and reproductive behavior of FAW feeding on castor oil leaves under laboratory conditions. Results revealed that the larval development lasted (12-19 days) while suffered (13%) mortality in their early instars. The percentage of larvae succeeded to pupal stage was (68%). When larvae reared in cohorts, about (3%) cannibalism only were recorded. The period required for adult emergency was (7.70 days) with (68.04 %) survival. Moreover, the average male to female sex ratio was (1: 1.06) with non-significantly difference. The wing malformation in females (15.67%) was significantly higher than males (1.82%), while the longevity was insignificantly affected. Females emerged earlier and began to lay their eggs through (3.33 days) and the oviposition continued up to (4-7 days). Single fertile female laid about (1225 – 2363 eggs) throughout its lifespan. The incubation period of egg stage was (2.19 days) with (97.92 %) of hatchability. Eventually, the total life period lasted about (23-30 days). Therefore, Cohort-based method recommended for rearing FAW in laboratory without mandatory effect on their larval cannibalism, survival and hence adult fecundity.