The present invention relates to polyamide-imides having head-to-tail backbone and more particularly, to polyamide-imimdes having head-to-tail ragularity to provide excellent heat and chemical resistance, physical and mechanical properties, processability, and gas permeability and selectivity. The polyamide-imides represented in the following formula (1) are obtained by direct polymerization, in the presence of dehydrating catalyst, of alone or as a mixture of 2 or above of monomers prepared by condensation of an amine compound having a nitro group with a carboxylic acid anhydride, ##STR1##