Background: The concept that eventually became unmet need of family planning was explored in 1960 when data from surveys of contraceptive KAP shoed a gap between some women’s reproductive intention and their contraceptive behavior. Aim: Objective of study was to estimate the socio economic and demographic patterns associated with the secondary infertility among those eligible couples who are in need of second child i.e. unmet need of family planning and to suggest remedial measures and advice to meet the needs of 2nd child. Materials and methods: The eligible couples are those, who are married, living together, having marital life and the age of the wife is in between 15 – 49 years. Simple random sampling technique was used to select 20 secondary infertility eligible couples from 450 ECs by making house to house survey. Results: The study results show that the upper middle and middle socio economic status is associated with the secondary infertility which is an obstacle to meet the needs of second child among the study group of eligible couples. Tukaram Kishanrao Pandve, P. Samuel Rajkumar, G. Nagaiah, Sayyad Tajmul, Bansode Arun, NS Inamdar. A study on the association of socio-demographic factors and secondary infertility among mothers with unmet needs of family planning in Sangareddy. IAIM, 2016; 3(7): 228-232. Page 229 Conclusion: the upper middle and middle socio economic status is associated with the secondary infertility which is an obstacle to meet the needs of second child among the study group of eligible couples.