The purpose of this study was to evaluate the periodic effect of desensitizing drug such as potassium oxalate(D.D.S. # I&II), strontium chloride (ZAROSEN)$^{(R)}$, and placebo group. The 193 teeth of 93 patients who had been complained dental hypersensitivity, and were divided into three groups by application agent and desensitizing treatment was completed. The interval of observation and treatment period were immediately, 1 week, 2 week, 3 week, 4 week, before and after treatment. The data was statistically analized and the results were as followed. 1. Group I showed best desensitizing effect to the stimuli, followed by Group II, Group III. 2. There was a significant difference (p < 0.005) in desensitizing effect among the Group I, Group III and Group II, Group III but there was no significant difference (p < 0.005) in Group I, Group II. 3. The cold stimuli was most effective in desensitization and there was a significant difference (p < 0.005) in cold, air-blast, but there was no significant difference (p < 0.005) in other stimuli. 4. There was no significant difference (p < 0.005) in effect of the desensitization of the cause of exposed dentine. 5. Anterior teeth was more effective than posterior teeth in desensitization and there was a significant difference (p < 0.005) between anterior teeth and posterior teeth. 6. In analysis of stimuli on the potassium oxalate, there was a significant difference (p < 0.005) in cold, air-blast but there was no significant difference (p < 0.005) in other stimuli.