Osteosarcoma is the most common malignant tumor primarily originated from bone, yet puerpera with osteosarcoma is exceedingly rare. We present here a case of a 27-year-old woman who was operated for femoral osteosarcoma 2 years ago. With emergency admission to Peking University Third Hospital she was diagnosed with recurrent osteosarcoma during the second trimester of pregnancy. As pregnancy might promote tumor development, the general principle demanded timely termination of pregnancy after diagnosis, but the patient insisted on giving up all her comprehensive cancer treatment. As a result, a well made plan for the protection of mother and child was carries out to perform cesarean delivery at the end of 32 weeks of gestation under general anesthesia. The baby was delivered successfully and the mother's condition was kept stable. This case highlighted the benefits of multidisciplinary cooperation and balanced the needs of the developing fetus with those of the mother.