The societies with high fertility rate exposed very less rate of son preference over daughter. But the fertility decline has a linkage of greater demand for son than daughter. In Manipur, a high proportion i.e. 31.2% of married women want more sons than daughters according to NFHS-3 which is declining from that of 36.5% in NFHS-2 and 43.4% in NFHS-1, so that, the factors associated with desire of more sons have caused high fertility indices in the state. The objective of this study is to investigate the socio-demographic determinants of fertility differential and the third birth transition.