Background Mutation and expression change of p21 WAF1/CIP1 may play a role in the growth of osteosarcoma. This study was to investigate the expression of the p21 WAF1/CIP1 gene in human osteosarcoma,p21 WAF1/CIP1 gene DNA sequence change and their relationships with the phenotype and clinical prognosis.Methods p21 WAF1/CIP1 gene in 10 normal people and the tumours of 45 osteosarcoma patients were examined using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) with silver staining. The PCR product with an abnormal strand was sequenced directly. The p21 WAF1/CIP1 gene mRNA and P21 protein of 45 cases of osteosarcoma were investigated by using in situ hybridization and immunohistochemistry,respectively. Results The occurrence of P21 protein in osteosarcoma was 17.78% (8/45),and p21 WAF1/CIP1 mRNA expression in osteosarcoma was 42.22% (19/45). The p21 WAF1/CIP1 gene DNA sequencing of amplified production showed that in p21 WAF1/CIP1 gene exon 3 of 36 cases of human osteosarcoma,there were 17 cases (47.22%) with C→T at position 609; 10 normal blood samples’ DNA sequence analysis yielded 8 cases (80.00%) with C→T at the same position. Conclusions Along with the increase of malignancy,the expression of p21 WAF1/CIP1 mRNA and P21 protein in osteosarcoma tends to decrease. It is uncommon for the p21 WAF1/CIP1 gene mutation to occur in human osteosarcoma. As a result, the possible existence of tumour subtypes of p21 WAF1/CIP1 gene mutation should be investigated. Our research leads to the location of p21 WAF1/CIP1 gene polymorphism of Chinese osteosarcoma patients,which can provide a basis for further research. Background Mutation and expression change of p21 WAF1 / CIP1 may play a role in the growth of osteosarcoma. This study was to investigate the expression of the p21 WAF1 / CIP1 gene in human osteosarcoma, p21 WAF1 / CIP1 gene DNA sequence change and their relationships with the phenotype and clinical prognosis. Methods p21 WAF1 / CIP1 gene in 10 normal people and the tumors of 45 osteosarcoma patients were examined using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) with silver staining. The PCR product with an abnormal strand The sequenced occurrence of P21 protein in osteosarcoma was 17.78% (8/45), and p21 protein in 45 cases of osteosarcoma were investigated by using in situ hybridization and immunohistochemistry, respectively. WAF1 / CIP1 mRNA expression in osteosarcoma was 42.22% (19/45). The p21 WAF1 / CIP1 gene DNA sequencing of amplified production showed that in p21 WAF1 / CIP1 gene Exon 3 of 36 cases of human osteosarcoma, there were 17 cases (47.22%) with C → T at position 609; 10 normal blood samples’ DNA sequence analysis yielded 8 cases (80.00%) with C → T at the same position. Conclusions Along with the increase of malignancy, the expression of p21 WAF1 / CIP1 mRNA and P21 protein in osteosarcoma tends to decrease. It is uncommon for the p21 WAF1 / CIP1 gene mutation to occur in human osteosarcoma. As a result, the possible existence of tumor Our research leads to the location of p21 WAF1 / CIP1 gene polymorphism of Chinese osteosarcoma patients, which can provide a basis for further research.