This paper aims to study the key factors affecting the process of business succession and post succession of family firms in Thailand. The purpose of this research paper is to identify the level of impacts and classify into four determinants i.e. the personal factor, the intra-family relationship factors, the context factors, and the financial factors. The paper also aims to study the relationship between the four factors and the post succession performance of family firms in Thailand. The methods use to assess the level of impacts of the factors on succession process of family firms in Thailand is by using the method of Structural Equation Model (SEM). The results of the SEM are based from the sample size 374 family business owners across various industries in Thailand. Context factors and personal factors are the two factors that have the highest levels of impact on the effectiveness of the succession process in comparison to the financial factors and the intra-family relationship. The results from this research paper also indicate that the succession process and the post-succession performance are positively related with a high level of impact.