A novel embryo evaluation system and microsensor devices have been developed using microcantilever-based biosensors. A holder-type piezoresistive cantilever was fabricated using a focused ion beam (FIB) to place and fix an embryo on the cantilever, and the monitoring system of the cantilever resonance frequency for measuring the embryo mass by the frequency sweep method was developed. The mass of a single 2-cell-stage mouse embryo was measured using the holder-type cantilever in a culture medium with calf serum. The resonance frequency of the cantilever before and after embryo placement was changed from 95.0 to 91.5 kHz. The resonance frequency was approximately constant during 20 min of monitoring. From the frequency change of −3.5 kHz, the mouse embryo mass was estimated to be about 4.4 ng. Although this value is smaller than the mass calculated from the volume of the mouse embryo and the density of culture medium, it indicates the possibility of measuring a single mouse embryo mass using a holder-type cantilever sensor system.