This study purports to investigate moral reasoning and ethical decision making among student nurses in the hypothetical moral dilemmas. The subjects consisted of 25 senior nursing students attending at a four-year college. Data were collected through self-reported questionnaires in November, 1993. The questionnaires included two kinds of tests. Rest's Defining Issues Test was adopted to measure the stage of moral development, which was classified with the stage 2 (instrumental relativist orientation), the stage 3 (interpersonal concordance), the stage 4 (law and order), the stage 5A (societal consensus), and the stage 5B (intuitional humanism). In particular, the level of principled thinking (P) was measured by summing those scores of the stages 5A, 5B, and 6. The possible range of P is 0 to 95. As for measuring the levels of morality and nursing dilemma, Crisham's Nursing Dilemma Test was adopted. This test generated the morality score(MS) and the dilemma score (DS). The data were analyzed by t-test, ANOVA, Kruskal-Wallis test, and Pearson correlation coefficients. The findings are following. 1. The mean score of P was 52.93 (SD=12.82). The mean score of the stage 5A was significantly higher than the scores of other stages (17.92, p=.0001). 2. The mean score of P was not significantly different by general characteristics of the students. Of the scores of each stage, only the mean score of the stage 3 revealed significant difference by the status of living with parents(p=.0283). The score was highest when "living with both parents"(15.22), which was followed by "living with no parents"(10.0), "living with father only"(9.0), and "living with mother only"(7.50). 3. With regard to the five dilemmas postulated such as forcing medication, performing cardiac pulmonary resuscitation, reporting a medication error, informing diagnosis to terminally ill adult, and providing new-nurse orientation, most students perceived them as moral dilemma rather than nonmoral one. Most students made a positive decision according to moral reasoning in the above situations except for providing new-nurse orientation. 4. The mean score of the MS was 3.30 and that of the DS was 3.32. These scores did not show significant difference with general characteristics of the students. 5. As for the correlations between moral reasoning and decision making, the score of the stage 5A was positively correlated with the scores of P(.74, p<.0001) and DS(.56, p<.001). Positive correlation was also observed between the scores of stage 2 and stage 4(.68, p<.0001). On the other hand, the score of P was negatively correlated with the scores of stage 3(-.47, p<.05) and of stage 4(-.55, p<.001). The score of the stage 5A was also negatively correlated with the score of the stage 6(-.42, p<.05).