In the last four decades and despite the 1997 crisis, Thailand has known as an impressive growth. One of the effects of this performance was to dramatically reduce absolute poverty. Thailand has reached the first of the Millennium goal in advance. However, the income distribution has become more unequal, especially in the last decades. Moreover, new categories of poor have emerged, probably not taken into account in statistics (migrant, minorities…). Presently, certain signs show that the pattern of economic growth is not anymore “pro-poor” as it has been in some periods in the past. Mechanisms of poverty reduction, such as welfare social policies are threatened and the looming economic crisis could hit poor particularly. This paper investigates the cross section of income distribution to see how the welfare of Thai households have evolved over time by exposing the great evolutions of income distribution and characterizing poverty in Thailand. It connects the elements of poverty analysis, income distribution and social contexts to explore how economic growth change in Thailand affects the poor during the last four decades, using series drawn from socio-economic surveys and international database. Also social impacts exposed to the poor are identified through patterns of social exclusion from the field studies.