In this paper, we demonstrate a compact silicon photonics based vibrometer using an on-chip photonic grating (OPG) based sensor. OPG works on the principle of interference where the motion of the cantilever is captured at the output as an intensity variation. The advantage of OPG based sensor over conventional Laser Doppler vibrometer is increased tolerance to alignment errors as both the grating and the cantilever can be integrated on a single chip. The grating parameters were optimized using 2D-FDTD to achieved maximum sensitivity to the displacement of a cantilever. OPG with on-chip germanium photodetector is studied, which indicates a sensitivity of 54 μW/nm. We experimentally demonstrate the feasibility of the proposed sensor that can achieve a displacement sensitivity of 5.3 μW/nm.