We investigated the size and mode dependencies of the resonance frequencies and quality factors of PMMA (polymethyl methacrylate) and PC (polycarbonate) cantilevers under atmospheric pressure in order to obtain fundamental data for polymer-based VOC (volatile organic compound) sensors. PMMA cantilevers and PC cantilevers are fabricated by hot embossing, bonding, and polishing techniques. Variations in the vibration mode result in large variations in the resonance frequencies and quality factors of these cantilevers. The measured resonance frequencies correlated well with the theoretical undamped resonance frequency of a flexural-vibrating cantilever. The measured quality factors varied from 10 to more than 100, depending on the vibration mode. A higher mode tended to exhibit a higher quality factor.