The purpose of this study is to determine the effect of childbirth preparation classes on self-efficacy in coping with labor pain in Thai primiparas. The nonprobability convenience sample consisted of sixty primiparas assigned to either a control or an experimental group (thirty in each group). In order to prevent crosscontamination, all control group data were collected before initiating enrollment of the experimental group. The control group participants received standard care and education. Participants in the experimental group attended three childbirth classes over three consecutive weeks. Data were collected at the beginning of week 1 to establish a baseline (pretest), at the end of the third class which is the end of the intervention (posttest), and at 24-48 hours after delivery (follow-up) using a demographic form, postnatal data form, and the Childbirth Self-efficacy Inventory. Overall, experimental group self-efficacy expectancy increased dramatically across three data points. In contrast, control group self-efficacy expectancy decreased dramatically across three data points. There was an interaction between time of selfefficacy expectancy measurement and group, F(1.33, 71.77) = 6.34, p < .05. Selfefficacy expectancy in the experimental group was significantly different than that of the control group, F(1, 54) = 14.66, p < .001. Outcome expectancy findings were different than self-efficacy expectancy results. Control group outcome expectancy decreased dramatically across three data points while the experimental group selfefficacy increased after the class and then decreased after the birth but was higher than baseline. There was an interaction between time of outcome expectancy measurement and group, F(1.72, 935.18) = 4.83, p < .05. Data at the follow-up or 24-48 hours after delivery revealed that only one woman from the control group received an analgesic during the birthing process. The groups did not differ in duration of labor and type of delivery. These findings indicate partial effect of childbirth preparation classes on self-efficacy in coping with labor pain. The relatively small effect size reflects the high degree of variability in issues surrounding a woman's experience of pain and measures related to self-efficacy in coping with labor pain. Additional research in this population is needed. / text