Thyroid cancer is one common endocrine malignancy with various pathological types. MicroRNAs (miRNAs) play essential roles in development, prognosis and treatment of thyroid cancer. However, the role of miR-17-5p in thyroid cancer progression and its mechanism remain poorly understood. The expressions of miR-17-5p and phosphatase and tensin homolog (PTEN) were measured in thyroid cancer tissues and cells by quantitative real-time polymerase chain reaction or western blot. Cell proliferation and apoptosis were detected by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay and flow cytometry, respectively. The protein levels of biomarkers in autophagy or protein kinase B (AKT)/mechanistic target of rapamycin (mTOR) pathway were analyzed by western blot. The interaction between miR-17-5p and PTEN was probed by luciferase activity assay. We found that miR-17-5p expression was elevated and PTEN level was reduced in thyroid cancer tissues and cells compared with their corresponding controls. Knockdown of miR-17-5p or overexpression of PTEN suppressed cell proliferation and autophagy but promoted apoptosis in thyroid cancer cells. PTEN was indicated as a target of miR-17-5p and its interference reversed abrogation of miR-17-5p-mediated inhibition of proliferation and autophagy and increase of apoptosis. Moreover, downregulation of miR-17-5p impeded the activation of AKT/mTOR pathway in thyroid cancer cells, which was attenuated by silencing PTEN. Our data supported that knockdown of miR-17-5p upregulated PTEN expression, therefore leading to suppression of the malignancy of thyroid cancer and inactivation of AKT/mTOR pathway, providing a novel avenue for treatment of thyroid cancer.