The headspace-GC/MS method is utilized to analyze volatile organic compounds (VOCs) in drinking water and environmental water. VOCs are easy to evaporate from the water, so they must be analyzed as quickly as possible after sampling.1) Accordingly, the analysis time must be as short as possible, particularly when many samples must be analyzed. The headspace sampler allows up to 12 samples to be heated simultaneously. Therefore, analytical conditions were investigated in order to shorten analysis time using the HS-20 headspace sampler. As a result, it was possible to measure five samples per hour.