INTRODUCTION: Attention monitoring and acceptance underlie the effects of mindfulness meditation. This study tested the feasibility and acceptability of an online mindfulness intervention for pregnant women as an approach to reduce depressive and anxious symptoms. METHOD: We developed an 8-week mindfulness intervention program that trained participants to monitor their internal and external experiences in an accepting way. The mindfulness course was based on the Wechat platform. This study was conducted in a women's hospital in China. A total of 123 women with scores on the Generalized Anxiety Disorder Scale and Patient Health Questionnaire suggesting mild or moderate symptoms of depression and anxiety were recruited from the outpatient department between April and June 2018. The participants were randomized to receive the mindfulness intervention or routine prenatal care. The Generalized Anxiety Disorder Scale, the Patient Health Questionnaire, and the Five Facets of Mindfulness Questionnaire were used to evaluate the levels of anxiety, depression, and mindfulness, respectively, before and after the intervention. RESULTS: Of the 123 women enrolled in this study, 10 in the intervention group and 11 in the control group did not complete the intervention. The retention rate and feedback suggested that the mindfulness intervention was feasible and acceptable among pregnant women. Participants in the intervention group showed greater declines in depressive and anxious symptoms compared with those in the control group, as well a significant improvement in mindfulness skills (eg, attention monitoring and acceptance). DISCUSSION: These results suggest that an online mindfulness intervention may be a promising technique to help women use mindfulness skills to reduce depressive and anxious symptoms. The mindfulness intervention could constitute part of the psychological care provided to pregnant women.