Celecoxib is a clinically available COX-2 inhibitor that has been reported to have antineoplastic activity. It has been proposed as a preventative agent for several types of early neoplastic lesions. Earlier studies have shown that sensitivity of prostatic carcinoma (PCa) to celecoxib is associated with apoptosis; however, these studies have not demonstrated adequately whether this effect is dependent on p53 status. We studied the relation between sensitivity to celecoxib and the phenotypic p53 status of PCa cells lines, LNCaP (wild type p53), PC3 (null p53) and DU145 (mutated p53). Cellular growth was assessed at 24, 48, 72 and 96 h after celecoxib treatment at concentrations of 0, 10, 30, 50, 70 and 100 μM using an MTT assay. Cellular proliferation (Ki-67 expression) was determined by immunocytochemistry. Phenotypic expression of p53 was analyzed by western blotting. The effects of celecoxib on cellular growth and its association with p53 were assessed after down-regulation of p53 using synthetic interfering RNAs (siRNA) in LNCaP cells. Expression of p53 and COX-2 at mRNA levels was assessed by quantitative real time polymerase reaction (qRT-PCR). We found that celecoxib inhibited cellular growth and proliferation in a dose-dependent manner in all three cell lines; LNCaP cells with a native p53 were the most sensitive to celecoxib. We observed a down- regulation effect on p53 in LNCaP cells exposed to ≥ 30 μM celecoxib for 72 h, but found no significant changes in the p53 levels of DU145 cells, which have a mutated p53. Reduced COX-2 expression was found with decreased p53 in LNCaP and PC-3 cells that were exposed to ≥ 20 μM of celecoxib for 72 h, but COX-2 expression was increased in DU145 cells. All three cell lines demonstrated pan-cytotoxicity when exposed to 100 μM celecoxib. When p53 expression was inhibited using siRNA in LNCaP cells, the inhibitory effects on cellular growth usually exerted by celecoxib were not changed significantly. Celecoxib reduces the growth of prostate cancer cell lines in part by decreasing proliferation, which suggests that the inhibition of growth of LNCaP cells by celecoxib is independent of normal levels of native p53.