New hexamethylenetetramine complexes of antimony and bismuth trichloride were synthesized through a solid phase reaction of hexamethylenetetramine and antimony or bismuth trichloride. The formula of the complex is MCl3(C6H12N4)2⋅H2O (M=Sb, Bi).The crystal structure of the complexes belongs to monoclinic system and the lattice parameters: a=1.249 nm, b=1.4583 nm, c=1.6780 nm andβ=91.78 for SbCl3(C6H12N4)2⋅H2O and a=1.3250 nm, b=1.3889 nm, c=1.7449 nm and β=98.94 for BiCl3(C6H12N4)2⋅H2O. Far-infrared spectra reveal that the antimony or bismuth ion is coordinated by the nitrogen atom of the hexamethylenetetramine. The thermal analysis also demonstrates the complex formation between the antimony or bismuth ion and hexamethylenetetramine. The intermediate and final residues in the thermal decomposition process have been analyzed to check the pyrolysis reaction.