The purpose of this study was to examine the effects of mouth care on the relief of oral discomfort undergoing radiation therapy patients. The nonequivalent control group time series design was used for this experimental study. The subjects were 32 patients who were receiving radiation therapy at P, D, G, hospital in Pusan from July 1, 1996 to August 31 1996. Among 32 subjects, 16 were placed in the experimental group and 16 in the control group. The subjects were contacted at the hospital, given an explanation of the study, and asked them to participate. The experimental group was educated according to oral care protocol. The data were collected through interviews, observations, and the health care records of the patients. The instruments were the "Perceived Oral Symptoms Assessment" by Chung, C. W. and "Oral Assessment Guide(OAG)" by Elers, Berger, & Petersen. SPSS PC+ was used to analyze the collected data. The general characteristics were analyzed by frequency, percentage, mean and standard deviations. The homogeneties between the experimental groups and control groups were tested by t-test and chi-square test. Perceived oral symptoms & OAG were tested by mean and standard deviations. The results of this research can summarized as follows : 1. Between two groups, the differences of perceived oral symptoms were not statistically significant (t=.0035, p=.9634). 2. In time series analysis the differences of perceived oral symptoms between two groups in the 7th week were only significant(t=5.0123, p=.0491). 3. The comparisons of each item in perceived oral symptoms, the differences between two groups were observed but they were not statistically significant. 4. Between two groups, the differences of OAG were not significant statistically(t=.0221, p=.8827). 5. In time series analysis, the differences of OAG between two groups were no statistically significant. 6. The comparisons of each item in OAG, the differences between two groups were observed but they were not statistically significant. In conclusion, this study could be utilized in patients care with radiation therapy although the results of the experiment were not accepted statistically.