We report the effects of growth conditions on the strain and crystalline quality of lowtemperature (LT) grown GaP films by gas-source molecular beam epitaxy. At temperatures below 160 °C, poly-crystalline GaP films are always obtained, regardless of the PH3 low rate used, while at temperatures above 160 °C, the material quality is affected by the PH3 flow rate. Contrary to compressively strained LT GaAs, high-resolution X-ray rocking curve measurement indicates a tensile strain of the LT GaP films, which is considered to be due to PGa antisite defects. The strain is found to be affected by the PH3 flow rate, the growth temperature, and post-growth annealing. Contrary to LT GaAs, no P precipitates are observed in cross-sectional transmission electron microscopy.