An on-axis laser Doppler vibrometer (LDV), where the direction of the incident beam is the same as the direction of the movement of the actuator, intrinsically offers an accurate dynamic measurement, although it cannot be currently applied to MEMS actuators with in-plane motion due to its limited access to the sidewall. The only currently available method is an off-axis LDV, which still shows serious measurement errors, depending on the target surface pattern of the device. In this paper, an on-axis fiber-optic LDV (FLDV) with a 45deg-angled optical fiber is proposed as a means of measuring the in-plane motion of a MEMS actuator. The device demonstrated displacements in the range between 6.5 mum at 2 Hz and 11.0 mum at 280 Hz, corresponding to the minimum and maximum velocities of 81.6 mum/s and 19.3 mm/s, respectively. The measurement capability of the proposed FLDV is then confirmed to cover the movement of most MEMS actuators such that it can greatly enhance the flexibility of dynamic measurements in MEMS actuators.