The Raman spectral shifts of methanol in pure methanol and methanol/water mixtures have been measured from room temperature up to 600 K under pressures of 10 or 20 MPa. In pure methanol, the gradual spectral changes of individual vibrational modes against the temperature indicate weakening of the intermethanol hydrogen bonding with temperature, but imply that it still remains at the critical temperature of methanol. In the methanol/water mixtures with low methanol contents, the Raman peaks of methanol do not move appreciably at temperatures lower than 600 K, which indicates that the methanol molecule is isolated in a water cage and the structure remains as it is up to 600 K.