A series of TiO₂ supported nano-Pd catalysts (Pd/TiO₂) were prepared and used for the N, N-dimethylation of different amines and nitro compounds with methanol under UV irradiation at room temperature. A wide range of N, N-dimethyl amines were one-pot synthesized with up to 98% by applying aliphatic secondary amines, aromatic primary amines, aliphatic primary amines and aromatic nitro compounds as starting materials. It is noteworthy that up to 90% yield of 4-chloro-N, N-dimethylaniline was obtained by adjusting the Pd loadings on the TiO₂ and the dehalogenation reaction was inhibited. Finally, a reaction mechanism is discussed, involving PhN = CH₂ and PhNHCH₃ as reaction intermediates.