The main purpose of this paper is to study the presence of internal habit formation in consumption behavior of Thai household through the total expenditure and other expenditures, including expenditures on food, non-alcohol beverage, alcohol beverage, tobacco, clothing, medicine, recreation equipment, education and transportation. The empirical tests are compared the consumption behavior under internal habit formation model in the middle class of Thai household, low income household and high income household. The estimated process uses Social-Economic Survey data over the period 1988 to 2006, and this data type is the cross-section data that it is adjusted to be the pooled cross-section data by matching the same type of household. The main results can be concluded that there is no existence of internal habit formation in the Thai economy. In addition, comparing between low income household and high income household, there are also no evidence of the internal habit formation. The analysis of the internal habit formation hypothesis that Thai household are divided from the education, the region, the socio-economy, the gender and the household status; moreover, they do not have the result of internal habit formation. Consequently, the second purpose is to test the credit constrained hypothesis in Thai consumption behavior. The conclusion of this research is to constraint the credit results in the main reason of reducing the consumer’s demand. So the consumption behavior is not influenced by the internal habit formation that it is affected through the total expenditure and other expenditures, in which are included food, non-alcohol beverage, alcohol beverage, clothing and education.