This dissertation presents the development of MEMS-based endoscopic OCT systems and the application for bladder cancer diagnosis at high resolution, noninvasively, and instantaneously. To enhance the image fidelity (e.g., SNR, dynamic range, and frame rate) critical to bladder cancer diagnosis, we proposed to utilize differential acousto-optic modulation technique (AOM) in combination with grating based rapid scanning optical delay (RSOD) to provide ultra-stable rapid axial scan of the reference mirror in time-domain OCT (TDOCT) system. In addition, we developed a spectral domain endoscopic OCT (SDOCT) system at 1.3 μm to enable higher imaging rate with improved dynamic range, and we proposed interpixel shift technique to enhance the effective field of view and dynamic range. Recent incorporation of Doppler OCT endoscopy to detect abnormal angiogenesis induced by carcinogenesis permits enhanced differentiation between malignant lesions and benign bladder lesions. To overcome the limitation of a relatively small field of view of endoscopic OCT (e.g., <5mm laterally per scan), we proposed fluorescence image guided OCT (FGOCT) to enhance the diagnostic efficacy in bladder. Results based on an ex vivo rat bladder carcinogenesis model showed enhanced diagnosis of bladder TCCs with sensitivity and specificity of 100% and 93%, respectively. Following successful ex vivo studies, we initiated in vivo clinical study. The experimental results based on 40 human cases have shown significantly improved diagnostic efficacy (91% sensitivity, 80% specificity) with no reported adverse effect, suggesting that OCT endoscopy is a very promising technique for bladder cancer diagnosis.