In the present study, oocyte development stages of the amphipod Pontogammarus maeoticus were determined based on gross morphology and histological appearance. For this purpose, the sampling was taken from the southern coasts of the Caspian Sea (Jefroodbeache, Guilan, Iran). Amphipods were transferred to a laboratory with some of their native sediment. Thirty pairs in 3 aquariums were maintained in controlled laboratory conditions with a temperature of 25±1 ºC, salinity of 9± 0.5 ppt and a 12:12 light:dark regime. Gravid females and females in precopula were prepared, processed and embedded in paraffin sectioned at 5 µm thickness and further stained by the hematoxylin-eosin general method. Based on the histological study, the oocyte development during the reproductive cycle has been classified into four different stages: 1) oogonia, 2) primary oocyte, 3) secondary oocyte (contains two substages: previtellogenic oocyte and vitellogenic oocyte) and 4) mature oocyte.