Abstract: The mass Spectra (EI) and the interpretation of five Mannich bases ofalkyl phenol are reported in this article. Three (n=3,4,5) of them 2,4, (C_2H_(2n+1))_2NCH_2(n-C_(12)H_(25))C_6H_3(OH)·HCl, (n=1,2,3,4,5) are newcompounds. No data about their mass spectra have been published in litera-ture. As a consequence of the interpretation of mass spectra (EI) we know thatthere are intense peak M~+., characteristic fragments both m/z 164+28(n-1)(n=1,2) with aliphatic amine-phenol structure and m/z 121 with the type oftropliumion-phenol structure. The I%～n curves of them show that the rela-tive intensity vary decreasingly (or increasingly) with n to be appeared ascarbon atom number contained in the alkyl combined with nitrogen atom. TheEI mass spectra show that a series of weak alkyl fragmentations characterizemass spectra of alkyl combined with nitrogen atom, and coupling ions for R~+and M-R~(?+). behave as cleavage feature of long chain alkyl (C_(12)H_(25)). As aresult of mass migration, metastabe ion detection (V/B, V/B~2 linked scan)and accurate mass, it were disscussed for respective fragmentationmechanism and the mass spectral feature of mutifunctional group moleculecontained -OH、-NR_2、-Ar、-ArOH、-ArCH_2NR_2、and -R.