The hydrogen bonding of 1:1 complexes formed between alanine and water molecules has been completely investigated in the present study using density functional theory, method B3LYP at varied basis set levels from 6-31G to 6-311++G(d,p) and the second-order Moller-Plesset perturbation method at the 6-3 1++G(d,p) level. Eight reasonable geometries on the potential energy hypersurface of the alanine and water system are considered with the global minimum. The optimized geometric parameters and interaction energies for various isomers at different levels are estimated. The infrared spectrum frequencies, IR intensities, and vibrational frequency shifts are reported. Finally, the solvent effects on the geometries of the alanine-water complexes have also been investigated using self-consistent reaction-field calculations at the B3LYP/6-311++G(d,p) level. The results indicate that the polarity of the solvent plays an important role in determining the structures and relative stabilities of different isomers.