An atomic absorption spectrophotometric dertermination of some cations namely sodium, potassium, calcium, magnesium, copper, iron and manganese in 30 drinking water samples was carried out using an acetylene-air flame. The drinking water samples were collected from the restaurants, supermarkets, and shops in Amphur Muang Chiang Mai Province. For the analysis of sodium, calcium and magnesium suitable ionization buffer solutions and/or releasing agents were added prior to analysis. It was found that the cation contents in the water samples were in the ranges of 0.33-17.07ppm, 0.00-11.40ppm, 0.19-37.61ppm, 0.00-8.92ppm, 0.00-0.04ppm, 0.01-0.31ppm and 0.01-0.05ppm for sodium, potassium, calcium, magnesium, copper, iron and manganese respectively. The heavy metal contents (copper, iron and manganese) were below the maximum allowable values for drinking water recommended by the Ministry of Public Health of Thailand.