Previous experimental evidence has suggested that fatty acid synthase (FASN) may be involved in cancer metastasis. However, its role has been poorly evaluated in osteosarcoma. The aim of this study was to investigate the correlation of FASN expression with pulmonary metastasis and the correlation of FASN expression with the Ki-67 antigen, a proliferation marker, in patients with osteosarcoma of the extremities. The expression of FASN protein and Ki-67 was detected by immunohistochemistry of biopsy tissues from 136 patients with osteosarcoma of the extremities and 21 cases of osteoenchondroma. Positive expression of the FASN protein was observed and located in the cytoplasm. The positive expression rate of FASN was 63.2% in osteosarcoma and 28.6% in osteoenchondroma (p<0.05). The expression levels of the FASN protein were higher in the cases with lung metastasis compared to those without metastasis (p<0.01). The percentage of Ki-67 stained nuclei in osteosarcoma with pulmonary metastasis and in those without was 43.43±10.05 and 25.41±6.68%, respectively (p<0.01). There was a positive correlation between FASN and Ki-67 protein expression in osteosarcoma (Spearman's rho, F=43.05, R=0.734). Therefore, FASN may be a promising target in the treatment of osteosarcoma metastasis.