The Five Facet Mindfulness Questionnaire (FFMQ) is a widely used measure in diverse populations. Despite the growing interest in mindfulness interventions for pregnant women, little research has examined the psychometric properties of mindfulness instruments in pregnant populations. In the present study, the reliability, validity, and factor structures of the FFMQ long and short forms were examined in a cross-sectional national survey of pregnant women (n = 857). The online survey also included measures of depression, anxiety, perceived stress, antenatal attachment, and social support. Mindfulness was significantly negatively correlated with depression, anxiety, and stress and positively correlated with maternal attachment and social support. The strongest correlations were found with the nonjudging of inner experience and acting with awareness facets of the FFMQ. Confirmatory factor analysis indicated that a correlated facets model with method effects best fits the data. This factor structure was consistent across four and five-factor models using the long and short forms of the FFMQ. Results support the validity of the FFMQ in pregnant women and suggest focusing on nonjudging of inner experience and acting with awareness facets as targets for cognitive approaches to improving mental health in pregnancy.