We demonstrated long-period grating (LPG) inscription on polymer functionalized optical microfibers and its applications in optical sensing. Optical microfibers were functionalized with ultraviolet-sensitive polymethyl methacrylate jackets and, thus, LPGs could be inscribed on optical microfibers via point-by-point ultraviolet laser exposure. For a 2 mm long microfiber LPG (MLPG) inscribed on optical microfibers with a diameter of 5.4 μm, a resonant dip of 15 dB at 1377 nm was observed. This MLPG showed a high sensitivity of strain and axial force, i.e., ?1.93 pm∕με and ?1.15 pm∕μN, respectively. Although the intrinsic temperature sensitivity of the LPGs is relatively low, i.e., ?12.75 pm∕°C, it can be increased to be ?385.11 pm∕°C by appropriate sealing. Benefiting from the small footprint and high sensitivity, MLPGs could have potential applications in optical sensing of strain, axial force, and temperature.