In this Letter, we demonstrate a sensitivity-enhanced strain sensor based on a shape-modulated multimode fiber (MMF). In contrast to conventional single-mode–multimode–single-mode (SMS) fiber structures, which typically contain a single cylindrical homogeneous MMF section, the shape of the MMF section in this investigation is modulated by lateral offset splicing of multiple MMF segments. Simulation results show that the designed shape-modulated MMF has a higher peak mechanical strain than that of a cylindrical MMF. Experimental results demonstrate that the strain sensitivity achieved by the shaped-modulated MMF-formed SMS fiber structure is as high as −55.63 pm/µε, which is 33 times higher than that for a cylindrical MMF-formed conventional SMS fiber structure at −1.65 pm/µε. This high sensitivity and low-fabrication cost SMS fiber sensor has the potential to be a promising candidate in precise strain measurement applications.