Introduction: The incidence of malignancy in pregnancy is reported to range approximately between 0.02% and 1%. Synovial sarcoma (SS) is a rare aggressive mesenchymal tumor for which there are no treatment guidelines during pregnancy. Case Report: The authors report a 23-year-old primigravida presenting, at 20+0 weeks of pregnancy, with a growing painful mass in the left thigh. The diagnosis of monophasic SS grade 3 was confirmed by the presence of SYT gene fusion. On MRI scan there was a heterogeneous localized mass of size 75×115×103 mm, but there was no evidence of distant metastases. Limb-sparing surgery with clear-surgical margins was performed at 26+3 weeks of pregnancy. Adjuvant chemotherapy with two cycles of doxorubicin was followed by delivery of normal child by caesarean section at 36+3 weeks of pregnancy. Adjuvant radiotherapy of total dose of 66 Gray to the site of the resection had been administered followed by two cycles of doxorubicin. Conclusion: The patient is free of recurrence six months after the completion of the treatment.