Several pilot studies have provided evidence that mindfulness-based intervention is beneficial during pregnancy, yet its effects in mothers during the early parenting period are unknown. The purpose of the present pilot study was to examine the effectiveness of a mindfulness-based intervention in breast-feeding mothers. We developed and tested an 8-week mindfulness-based intervention aimed at improving maternal self-efficacy, mindfulness, self-compassion, satisfaction with life, and subjective happiness, and at reducing psychological distress. A randomized controlled, between-groups design was used with treatment and control groups (n = 26) and pretest and posttest measures. ANCOVA results indicated that, compared to the control group, mothers in the treatment group scored significantly higher on maternal self-efficacy, some dimensions of mindfulness (observing, acting with awareness, non-judging, and non-reactivity), and self-compassion (self-kindness, mindfulness, over-identification, and total self-compassion). In addition, mothers who received the treatment exhibited significantly less anxiety, stress, and psychological distress. The results supported previous research findings about the benefits of mindfulness-based intervention in women from the perinatal and postpartum periods through the early parenting period. Additional research is needed to validate our findings in non-breast-feeding mothers and to examine the intervention's indirect benefits in terms of family relationships and child development.