Long-period gratings, which display sensitivity to ambient temperature variations, are proposed as sensors. Therefore, full temperature characterisation is essential. In this paper, the effects of temperature upon the spectral profiles of two sets of long period gratings (LPGs) of different periods are investigated. The results obtained show that the shorter-period LPGs were found to be less sensitive than the longer-period LPGS over identical temperature ranges. The coupling wavelength shifts due to temperature are also seen to be linear and in opposite directions in each set of LPGs.