In the present study it was aimed to investigate the frequency of K-RAS mutation in the human bladder transitional cell carcinoma. For this purpose, tissue specimens obtained from the patients with bladder tumors. Genomic DNAs were isolated and then PCR-SSCP analysis of K-RAS gene were performed. A heterozygous deleted mutation was detected in K-RAS oncogene (exon 2) in agarose gel electrophoresis in one patient and point or substitution mutations are detected using single strand conformational polymorphism (SSCP) in other different patients with bladder cancer (4/14). In conclusion, the frequency of K-RAS mutation is not rare and the role of this mutation in oncogenesis and in infiltration of the urinary bladder wall needs to be confirmed in a larger study.