This study is to analyse the causes of accident in small and medium-sized construction sites and to provide prevention strategies and system improvement guidance. Although occupational safety and health act regulates the standards and installations of temporary structures, about an half of construction accidents were caused by poor temporary structures such as guardrails, scaffolds, work platforms, etc. It investigated 51 construction sites which is located in metropolitan area by asking a series of questions including their knowledge about regulations and opinions about prevention strategies. The result shows that many of the respondents do not have sufficient understandings about the regulations, and it implies that education and training must be reinforced in order to enhance the safety-awareness and to develop the comprehension of regulations.