This study is for measuring how much high-school students’ service learning affects to their senses of ego-identity, school adjustment, and career maturity. The subjects of this study are 674 high-school students(male 306, female 368). SPSS Statistics for Windows 17.0 was the analyzing tool for surveying data. The researcher measured Cronbach α coefficient firstly for the reliability of each survey scale. Independent-Samples T-test & One-Way ANOVA were used for the Comparing Means, and Scheff? method for the Post Hoc Multiple Comparisons. Then, the Regression Analysis was used for the elucidating ratio that says how much the independent variable exercises influences over the dependent variable. The results of the research can be summarized as follows: First, service learning participants had a higher mean in ego-identity, school adjustment, and career maturity than non-participants. Therefore, high-school student’s service learning experience exercised a affirmative influence over the ego-identity, school adjustment, and career maturity. Second, ‘Worth doing of service’ which is one of the service motives was a meaningful factor statistically in ego-identity, and school adjustment. Third, students who were higher in the sense of voluntary service satisfaction were figured out also to be higher meaningfully in total ego-identity value and in its 4 out of 5 subordinate variables than lower service satisfaction students. In accordance with these results, when high-school students participate in voluntary service with more worthwhile doing, larger affirmative development in the sense of ego-identity, school adjustment, and career maturity could be expected. Therefore for the further result, the researcher recommends that there should be a study on between the relation of the actual conditions of high-school students’ voluntary service and the outcome of the experimental service learning practices.