Cell microinjection plays an important role in biological and medical fields. As compared with manual cell microinjection and position-based robotic cell microinjection, force-assisted robotic cell microinjection can improve the success rate and survival rate of the injected cells. In this paper, a novel force-sensing cell microinjector is proposed with a piezoresistive force sensor embedded in soft-material-based flexure mechanism. The soft flexures act as fixed-guided beams, which are introduced to achieve the force measurement with high sensitivity in pure one-degree-of-freedom direction. The microinjector is developed by considering the installation and replacement issues of the micropipette and the connection between the micropipette and the tube of compressed air. Four different prototypes of the cell microinjector with force sensor are fabricated, calibrated, and compared. Results show that the resolution and measurement ranges of an embedded force sensor are 0.65 mN and 16.5 mN, respectively. Experimental study on microinjection of crab eggs is conducted to validate the performance of the fabricated microinjector in practice.