A family is considered as an initial institution of social relation, which is a fundamental wheel of all economic activities as well. Unfortunately this primary economic and social institution is facing severe challenge in both developed and developing countries although the nature and reasons of its fragility are different. In this paper I have tried to develop a theoretical reason of changing family structure in developed and developing countries via simple utility maximisation principle and then add some empirical evidences to support my propositions. My conclusion says that advanced social security support and high wage rate in developed countries motivates elderly generation to live in a nuclear family setting while least social security and low wage rate in developing countries we come across this tendency in working generation. This conclusion has been empirically supported using cross-section pooled data from developed, newly developed, and least developed seventy five countries through over the world.