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Optical coherence tomography (OCT) is a novel technique that enables noninvasive cross-sectional imaging of biological tissues. Because of its high resolution (approximately 10 microm), superior dynamic range (140 dB in our case) and up to 2-3 mm penetration depth, OCT is potentially useful for noninvasive screening of superficial lesions. Bladder cancer arises within the transitional epithelium. Despite the ability to visualize the epithelium via cystoscopy, it is often difficult to detect early epithelial cancers and to determine their penetration to the underlying layers. To investigate the potential of OCT to enhance imaging of bladder cancers and other epithelial lesions, we applied OCT to normal and diseased bladder epithelium, and correlated the results with histological findings. OCT images of porcine bladder (a close homolog of human bladder) confirm the ability of this method to image human tissues. To determine whether OCT can track the course of bladder cancer, a standard rat model of bladder cancer in which Fisher rats are exposed to methyl-nitroso-urea (MNU), was followed both with OCT and histological studies. Our results show that the micro morphology of porcine bladder such as the urothelium, submucosa and muscles is identified by OCT and well correlated with the histological evaluations. OCT detected edema, inflammatory infiltrates, and submucosal blood congestion as well as the abnormal growth of urothelium (e.g., papillary hyperplasia and carcinomas). By contrast, surface imaging, which resembles cystoscopy, provided far less sensitivity and resolution than OCT. This is the first OCT study of any tumor documented in a systematic fashion, and the results suggest the potential of OCT for the noninvasive diagnosis of both bladder inflammatory lesions and early urothelial abnormalities, which conventional cystoscopy often misses, by imaging characterization of the increases in urothelial thickening and backscattering. However, because of the depth limitation, OCT may have limited applications in staging the invasion of higher-state urothelial cancers, especially for papillary carcinomas.