Rich people in Thailand are enjoying higher shares in income transfer than their poor counterparts. This strange phenomenon implies the malfunction of the Thai social security system. Studies on the relationship between social security development and social, economic and political factors are also very limited. These evident constraints are the rationales for this study. A comparative study was chosen because the justification of social security problems would be more objectively valid if r000esearch findings were compared with external criteria. In addition, comparative analysis would clearly pinpoint possible factors that influenced social security development in Thailand. Like many comparative studies, this investigation did not expect only to identify possible influential factors, but it also intended to learn how the modern social security system could be established in a more developed country. However, the findings would be more adaptable if they were transferred from a country that was economically and culturally close to Thailand. By these reasons, Australia, instead of other Western countries, was more appropriate to be the case for comparison. After reviewing theoretical and empirical literature, the research methodology was designed. Basically, the study applied both qualitative and quantitative methods in analysing data gathered from Thailand and Australia. Comparative evidence shows many problems in social security provisions in Thailand. Relatively narrow coverage, low quality and quantity of benefits and services, higher financial burdens borne by people, and marginal welfare rights are the important indications of the severity of the problems. Many factors are responsible for the existence of these problems. The problematic system of social security was partly the legacy of historical development. The effects of historical roots are intensified by many contemporary factors. Undesirable social values, volatile economic growth, late industrialisation and the defeat of socialism are the four major factors that account for the undeveloped social security system. The influences of the four major factors are supported by another four less crucial ones. These supporting factors comprise the elite�s agenda, workers� power, weak non-governmental organisations and population growth. The findings in both Thailand and Australia similarly indicate that religious institutions and colonial influence do not produce significant effects upon social security development. The comparative findings provide valuable guidelines for the suggestions of system development. Several findings help extend existing theoretical explanations of social security development as well. The study recommends comprehensive operational strategies for the improvement of Thai social security. The study made its final suggestion on the importance of applied research based on Western knowledge and experiences for the improvement of Thai social security.