^1H NMR spectra of amine borane, <(CH_3)>_<3-n> H_nN･BH_3 and amine boron trifluoride, <(CH_3)>_<3-n>H_nN･BF_3 adducts were observed. ^1H chemical shifts of methyl groups occur at a higher field as the methyl group successively substituted for hydrogen on nitrogen. With respect to trimethylamine, both BH_3 and BF_3 bases are considered to be comparable acids. These results lead to a good relation between chemical shifts in BF_3 group and variations in structure on amine boron trifluoride adducts.