Precise and objective measurements of tumor response have yet to be standardized in the mouse orthotopic bladder cancer model. In this study, we used image analysis and green fluorescent protein (GFP) to objectively measure tumor size in response to chemotherapy. KU-7 human bladder cancer cells transfected with GFP were intravesically inoculated into 8-week-old female nude mice. Fourteen days after tumor cell inoculation, the mice were assigned into a control (PBS) group or a doxorubicin (conc. 1.0 mg/ml) treatment group and received a single instillation of treatment. Fourteen days after treatment, the bladders were surgically exposed and fluorescent images were captured and later analyzed using image analysis. Bladders were processed for histological examination. Tumor incidence determined by GFP expression and histology was 100 and 80%, respectively, in the doxorubicin treatment group. A 9-fold (histology) vs. 12-fold (GFP expression) difference in tumor regression measured by tumor area (P<0.05) and a 5-fold (histology) vs. 9-fold (GFP expression) difference in tumor regression measured by the percent of tumor area in the bladder (P<0.001) were observed in the doxorubicin treatment group. Our findings suggest that using image analysis provides a precise, sensitive and objective means to measure tumor growth and treatment response in the mouse orthotopic bladder cancer model in lieu of histological methods. Consequently, the number of mice required in an experiment can be reduced since tissue samples are not needed for histology, thus making tissue samples readily available for additional assays in both a labor-effective and cost-effective manner.