Background Mutation and expression change of p21WAF1/CIPI may play a role in the growth of osteosarcoma. This study was to investigate the expression of the p21WAF1/CIPI gene in human osteosarcoma, p21WAFl/CIPI gene DNA sequence change and their relationships with the phenotype and clinical prognosis. Methods p21WAF1/CIPI 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 p21WAF1/CIPI gene mRNA and P21 protein of 45 cases of osteosarcoma were investigated by using in situ hybridization and mmunohistochemistry, respectively. Results The occurrence of P21 protein in osteosarcoma was 17.78% (8/45), and p21WAFl/CIPI mRNA expression in osteosarcoma was 42.22% (19/45). The p21WAFl/CIPI gene DNA sequencing of amplified production showed that in p21WAF1/CIPI 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 p21WAF1/CIPI mRNA and P21 protein in osteosarcoma tends to decrease. It is uncommon for the p21WAF1/CIPI gene mutation to occur in human osteosarcoma. As a result, the possible existence of tumour subtypes of p21WAF1/CIPI gene mutation should be investigated. Our research leads to the location of p21WAF1/CIPI gene polymorphism of Chinese osteosarcoma patients, which can provide a basis for further research.