The study of reproductive biology is a prerequisite for fishery management and conservation. The current study aimed to compile all available information on the reproductive biology of the grey mullet, Mugil cephalus from two geographical regions of India, Cochin backwaters (west coast; n= 362) and Pulicat (east coast; n= 223) southern India to decipher the possible differences in reproductive and biological attributes between the geographical groups. The LWR showed isometric growth (b= 3.08) for females on the west coast and positive allometric growth (b= 3.338) on the east coast, whereas the males showed negative allometric growth on both coasts. The sex ratio (male: female) recorded in this study was 1: 1.2 on the west coast and was well balanced. On the east coast, the sex ratio was 1: 2.09 and deviated significantly from the expected 1: 1 ratio. The gonadal morphology and developmental pattern were the same for both groups of M. cephalus. The length at maturity values of both males (L 50= 349.3 mm TL on the west coast and 375.8 mm TL on the east coast) and female (L 50= 437.6 mm TL in the west coast and 394.9 mm TL in the east coast) showed a significant difference between two groups. Seasonal distribution of GSI and maturity stages suggested that the spawning period of M. cephalus was between May and July coinciding with the onset of the southwest monsoon on the west coast while on the east coast it was between December and January months during the north-east monsoon. The reproductive isolation and philopatry in west and east coast M. cephalus groups are discussed based on the observations on the spatio-temporal distribution of fishes in the sampling areas.