The purpose of the study is to analyze the effects of a mat Pilates intervention on the postural alignment and balance of breast cancer women receiving hormone therapy. A two-arm randomized clinical trial included 34 breast cancer survivors divided randomly between a mat Pilates group (n = 18), that performed 16 weeks of mat Pilates exercises, and a control group (n = 16), who were invited to maintain their daily routine activities and received three educational sessions. Data collection occurred at baseline and at post-intervention time. The postural alignment was assessed using the Postural Assessment Software (SAPO) and the balance was assessed by the MINIBESTest. When the two-way ANOVA was performed on postural alignment results, a significant statistical difference was found in the angle between acromions and the anterior-superior iliac spines of the mat Pilates group (p = 0.036). When compared to the post-intervention period, the mat Pilates method had an improved horizontal alignment of the anterior-superior iliac spines (p = 0.039) and vertical alignment of the acromion head on the right side (p = 0,016). Also, the participants of the Pilates group showed a significant statistical difference in the balance (p = 0.034). The control group had an improved vertical trunk alignment on the left side (p = 0,048). The control group and the mat Pilates method group improved in some aspects, however the mat Pilates method was effective in improving the postural alignment and the balance of breast cancer survivors receiving hormone therapy and may be recommended in oncological rehabilitation as a type of complementary therapy.