The substrate temperature is an important parameter in thin him deposition regardless of the deposition technique being used to deposit thin films. In this paper the effects of the substrate temperature on the properties of CuIn0.75Ga0.25Se2 (CIGS) thin films are reported, Structure, surface morphology and optical properties of CIGS thin films deposited at various substrate temperatures have been investigated using a number of analysis techniques. X-ray diffraction (XRD) analysis at room temperature shows that CIGS films exhibit a strong [112] preferred orientation. As expected, at higher substrate temperatures the films displayed a higher degree of crystallinity, The [112] peak was also enhanced and other CIGS peaks appeared simultaneously. These results were supported by experimental work using Raman spectroscopy. The Raman spectra of the as-grown CIGS thin films show only the A(1) mode peak. The intensity of this peak was enhanced at higher deposition temperatures. Scanning electron microscopy (SERI) results revealed very small grains separated by larger Voids in films fabricated at room temperature. When the substrate temperature was increased the average grain size also increased together with a reduction in the number and size of the voids. The deposition temperature also had a significant influence on the transmission spectra.