A vital signs monitor based on few-mode fiber (FMF) is presented in this paper. Two types of FMF, dual-mode fiber (DMF) and four-mode fiber are respectively utilized for vital signs monitoring. For DMF, core-offset distance between lead-in single mode fiber (SMF) and DMF was optimized numerically, the results of which agree very well with experiments and respiration ratio can be measured successfully with acceptable extinction ratio. For four-mode fiber, core-offset mode excitation method with optimized parameters is also utilized to excite four types of modes, LP01, LP11, LP21 and LP02, which realizes the modal interference enhancement and the extinction ratio can reach 10 dB. Breath signals can be also detected using this structure. As demonstrated in this paper, FMF-based sensor could provide a promising candidate for fiber-optic biomedical application.