In this study, cochlear mechanics of four different species (gerbil, chinchilla, cat, and human) are studied through physiologically-based cochlear model. The present work serves as an extension of previous cochlear modeling research by improving on the older models and incorporating new imaging technologies.;By virtue of the three-dimensional cochlear model, intracochlear pressure in the ST is obtained by adding the fast wave to the traveling pressure slow wave. From the intracochlear pressure simulation, derived quantities: (1) BM velocity, (2) pressure difference across OC, and (3) OC impedance in the base, are calculated by following Olsons estimation (1998). These quantities are compared with animal measurements and showed excellent agreement. From the validated gerbil cochlear model, the exact theoretical OC impedance is obtained and compared with the estimated theoretical OC impedance. By comparing exact and estimated theoretical OC impedances, a fast wave component in the estimated theoretical OC impedance is founded and it causes phase fluctuation out of the reasonable range (negative real part of impedance in the passive response) and notches in the estimated theoretical OC impedance. The exact theoretical OC impedance from the active model shows negative real components which represents active process from the OHCs motility. Measurements of the spatial distribution of the response of the BM at a fixed frequency (Ren, 2002) and the frequency distribution at a fixed point (Ren and Nuttall, 2001) offer an unusual opportunity for validation of model calculations. The comparison of results from the model and experiment is promising. Using a single set of anatomically based parameters, the model predicts several significant features of cochlear response. The CF-to-place map in the passive model, frequency and spatial responses of BM velocity were in close agreement with those observed in animal measurement.;Cochlear physiologies for four species; gerbil,