Legionella is important human pathogen.The surveillance for legionella in water reservoir is suggested. Contamination by legionella in natural hot springs may pose a significant health risk to people who use such water for recreation activities.The aim of this work is to summarize the pattern on legionella contamination in hot spring pools in Thailand. According to the search, there are 13 on radon in 83 hot spring pools in Thailand (December 2007). The number of hot springs with legionella contamination is equal to 48 (57.8 %). In addition to legionella, situation on free living amoeba in hot spring pools in Thailand is also presented in this article.