Material and Method: This is a quasi-experimental study which based on a pretest-posttest design with group comparison. The participants were primiparous adolescent mothers aged 15-19 years who attended at antenatal care clinic, delivered and came for postpartum check-up at 6 weeks after delivery at Thammasat University Hospital from December 2013 to March 2014.

Results: Sixty adolescent mothers were selected through inclusion criteria and divided equally to study and control group. Study group participated in the effects of the promoting self-efficacy program combined with standard nursing care. Control group received only standard nursing care from the same nursing staff. Demographic data of both groups had no statistical difference. Mean scores on oral contraceptive self-efficacy (OCSE) and oral contraceptive used behavior (OCUB) of study group were higher than control group with a statistical significance (p<0.001) at 12 weeks postpartum.

Conclusion: Adolescent mothers had a high risk of unintended pregnancy due to inconsistent oral contraceptive usage. Promoting self-efficacy program regarding oral contraceptive behavior should be integrated to standard nursing care practice. This program could encourage adolescent mothers to engage correct and continuous oral contraceptive usage.

Keywords: Adolescent mother, Promoting self-efficacy, Oral contraceptive used behavior