Tenualosa ilisha is locally known as Nga tha lauk in Myanmar and as hilsa shad in English. It occurs in the coastal shelf, estuaries, brackish waters and freshwater rivers. It is the most widespread species found from north Sumatra in the east to Kuwait in the west and the basis of important fisheries in Bangladesh, India, Myanmar, Pakistan and Kuwait. A total of 240 samples of T. ilisha were studied which were obtained from Yangon and Ayeyarwaddy Division in Myanmar during the study period from November 2003 to July 2005. Total body length, standard length, body weight and gonad weight were recorded to analyze the Gonosomatic indices (GSI). Condition factors (K) were also determined to confirm the results of GSI. The GSI value of female T. ilisha was the highest (17.2±4.39) in October and the second highest was (13.52± 5.54) in May. Therefore, there were two peak seasons of the species in October and May. Histological studies were conducted to confirm the reproductive stage. According to the GSI and histological studies, five stages of cyclical changes i.e. maturity in March and August, pre-spawning in April and September, spawning in May and October, post spawning in June and December, resting in July and January were found in T. ilisha. According to the sample collection and information obtained, the population of T. ilisha species are assumed to be decreasing in the wild. It indicated to avoid catching these species during their peak of the breeding seasons. Thus, awareness is needed to sustain this species in future.