<p>Myanmar possesses a high potential for geothermal resources, considering the distribution and development of the resources in its neighboring countries. For effective utilization and sustainable development of geothermal resources, fundamental studies, including water quality characterization and analysis of the formation mechanism for hot springs, are essential; however, previous studies are limited and lacking, especially in Myanmar. In this study, field investigations were conducted in the Mon, Shan, and Kayin States of southeastern Myanmar. The water quality of 12 hot springs at seven sites was characterized to determine the origin and formation of water quality. Stable isotope ratios of oxygen and hydrogen, considering the global and local meteoric water lines in Yangon City, suggest that most of the hot spring water is of precipitation origin. Six main water quality types, Ca-SO₄; Na-SO₄; Na-Cl; Na-Cl, SO₄; Na-Cl, HCO₃; and Na-HCO₃, were observed, which significantly differed from the typical shallow groundwater quality (Ca-HCO₃-dominated type). Notably, the water quality of some high-salinity hot springs was similar to that of seawater (Na-Cl-dominated type). Based on laboratory analysis, all water quality parameters of the major cations and anions, including HCO₃^– concentration, stable isotope ratios, and trace elements, suggested that the high-salinity hot springs can be related to altered seawater. Further comprehensive investigations of known and newly developed hot springs are required to accelerate the effective utilization and sustainable development of geothermal resources in Myanmar.</p>