Equitable health financing was embodied in the reform strategies of Thailand's health care system when the country moved towards implementing the Universal Coverage (UC) policy in 2001. This study aimed to measure the pattern of household out-of-pocket payments for health care and to examine the financial catastrophe and impoverishment due to such payments during the transitional period (pre- and post-Universal Coverage policy implementation) in Thailand. This study used the nationally representative Socioeconomic Surveys in 2000 (pre-UC), 2002, and 2004 (post-UC), which contained data from 24747, 34758 and 34843 individual households, respectively. The proportion of out-of-pocket payments for health care as a share of household living standards among Thai households shows a decreasing pattern during the observed period. Moreover, the incidence and intensity of catastrophic payments for health care decline from the pre-UC to post-UC period. The distribution of incidence and the intensity of catastrophic payments for health care across quintiles also indicate that the lower quintile group (1st and 2nd quintiles) incurs lower catastrophic health care payments compared to the higher quintile group. The UC policy is also effective in preventing impoverishment due to out-of-pocket payments for health care since both the poverty headcount and poverty gap decline from the pre-UC to post-UC period. This study provides important evidence that the UC policy implementation is a valuable social protection and safety net strategy that contributes to the prevention of financial catastrophe and impoverishment due to out-of-pocket payments for health care. In conclusion, the UC policy in Thailand achieves one of the goals of improving the health system through equitable health care financing by reducing financial catastrophe and impoverishment due to out-of-pocket payments for health care.