The human population of world is growing very rapidly and facing a crisis due to over population. In the study of demography, fertility is the most important and perhaps the most complicated aspect than any other aspect of the population. There is a paramount need for the study of components of population growth i.e. fertility, mortality and migration. There is a very sharp reduction in mortality rates and fairly slow declines in fertility rates in Pakistan. This situation presents an alarming vision of the future, because fertility affects the population in variety of ways. So it should be checked so that it would make the country prosperous. The present study “differential fertility with special reference to social stratification” was conducted in Southern Punjab. Three main districts of Southern Punjab Multan, Bahawalpur and Dera Ghazi Khan were selected for the study. Culturally the Southern Punjab is almost the same in nature, but there are too much socio-economic differences between these areas and among the people. Stratified method of sampling was used. The main objectives of the present study were to find out the various socio-economic factors that lead to higher fertility and determine the fertility differential among the various couples according to social stratification. The variation in fertility is caused by various factors such as, educational attainment, economic status, occupation, age, age at the time of marriage, marital period, employment status of woman, religious, race, family structure, health status, etc. These factors are related to each other one being influenced by the other. In the present study 600 respondents were interviewed, the interview schedule technique of data collection was used. The analysis of data was made by using statistical package of social science. Six hypotheses were formulated and five of them were proved and only one hypothesis was disproved.