A plasma emission spectrophotometer "Spectraspan" (low power d. c. plasma arc, operating on argon) was evaluated for boron determination in thermal waters. The influence of acids (hydrochloric, nitric and sulfuric acids) and several metallic ions (Na(+). K(+), Mg(2+). Ca(2+)) on emission intensity was studied. There was a linear relationship between emission intensity and boron content from 0 to 500 mg/l. Boron in thermal waters was easily determined by standard addition method. Precision. coefficient of variance and recoveries of known amount of boron added to the sample for 11 repricate analyses were 0.12μg/ml, 2.02%, 95.0-101.7%, respectively. Boron content of 27 thermal waters in the Sanin district was determined. and the highest B content in the sample waters were 8.8 mg/l (Tottori spa) in Tottori Prefecture and 14.6-25.0 mg/l (the thermal springs at the foot of Mt. Sanbe. a non-active quaternary volcano) in Shimane Prefecture. The relationships between B content and water temperature, B content and pH value were not recognized. Significantly positive correlationship was observed between Band Li contents.