Due to the stimulated emission amplification, lasers with excellent characteristics, including the high energy density, ultra-narrow spectral linewidth, and high directionality, are extremely favorable for sensing, detection, and imaging. Bringing these merits into the micro/nano scale, micro/nano lasers with miniaturized device sizes further enable outstanding spatial and temporal confinement, greatly boosting the light-matter interaction and bridging the size mismatch between light and biomolecules. Thanks to these advantages, micro/nano lasers have drawn widespread attention and opened new opportunities for a variety of biomedical and biochemical applications. In this paper, we review recent developments in biomolecular sensing and cellular analysis based on micro/nano lasers. We first describe the fundamental building blocks of micro/nano lasers, with discussions on gain material considerations, cavity structures, and pumping. We then review recent applications using micro/nano lasers as biosensors and bioprobes, including biomolecule (mainly proteins and DNAs) sensing, wavelength-multiplexed cell labeling/tracking/probing, and high-resolution cellular/tissue bioimaging. Finally, an outlook of the challenges and potential developments of micro/nano lasers for biological sensing and clinical applications is provided.