Monolayer molybdenum disulfide (MoS2) is an emerging two-dimensional material beyond graphene, which could potentially be applicable to lightweight, flexible optoelectronic device. In this study, we have demonstrated a planar metal-semiconductor-metal (MSM) photodetectors based on large area monolayer MoS2. The monolayer MoS2 was grown via chemical vapor deposition method, showing excellent structural and optical properties. The current-voltage measurement was characterized at various monochromatic lights in visible spectrum. The device exhibited good responsivity ~7.7 mA/W for wavelength of ~470 nm, which is relatively comparative to mechanical exfoliated monolayer MoS2 based photodetectors. Additionally, the photoresponse measurement showed that the rise/fall time was about 1/0.7 s.