Hypothesis. Qigong exercise is a popular method for relieving the side effects of conventional cancer treatments in survivors of breast cancer, yet its effects are not empirically assessed. This study aimed to investigate the effects of qigong exercise on upper limb lymphedema, arterial resistance, and blood flow velocity in survivors with breast cancer and mastectomy. Study Design. This study was conducted as a prospective clinical trial. Methods. Eleven survivors of breast cancer with qigong experience (mean age = 58.3 ± 10.1 years) were assigned to the experimental group and 12 survivors of breast cancer without qigong experience (mean age = 53.8 ± 4.2 years) were assigned to the control group. They all had breast cancerrelated lymphedema. All procedures were completed within one session. After baseline measurements were taken, the experimental group performed 18 Forms Tai Chi Internal Qigong for approximately 6 minutes while the control group rested for similar duration in a sitting position. Both groups were then reassessed. All participants were measured on their affected upper limb circumference (by using tape measures), peripheral arterial resistance, and blood flow velocities (using a Doppler ultrasound machine). Results. The between-group differences were not significant for all outcome measures at baseline (P > .05). The circumferences of the affected upper arm, elbow, forearm and wrist decreased after qigong exercise (P < .05). However, no significant difference was found in the circumference measures between the 2 groups posttest (P > .0125). In terms of vascular outcomes, the resistance index decreased and the maximum systolic arterial blood flow velocity (SV) and minimum diastolic arterial blood flow velocity (DV) increased significantly after qigong exercise (P < .05). The between-group difference was close to significant for SV (P = .018) and was significant for DV (P < .001) posttest. Conclusion. Qigong exercise could reduce conventional cancer therapy side effects such as upper limb lymphedema and poor circulatory status in survivors of breast cancer. However, such effects may be temporary, and further studies must be conducted to explore longer term effects.