A homopoly(ester-imide) was prepared from N-(10-carboxydecanyl) trimellitic imide and hydroquinone diacetate via melt transesterification condensation. The phase transition behavior was checked with DSC, rheometry, and polarized light microscopy experiments. The homopoly(ester-imide) showed only crystallization transition when it was cooled from isotropic melt. Nevertheless it showed thread-like texture when quenched below crystallization temperature. In order to check mesophase formation, copoly(ester-imide)s containing both 10 and 4 methylene units were made varying the mole ratio of N-( 10-carboxydecanyl) trimellitic imide to N-(4-carboxybutyl) trimellitic imide. All copoly(ester-imide)s exhibited nematic phase transition and, in particular, they showed monotropic nematic transition, when they had large portion of 10 methylene unit. The nematic to isotropic phase transition temperature of homopoly(ester-imide) was obtained extrapolating those of copoly(ester-imide)s and matched well with the crystallization temperature of the homopoly(ester-imide). (C) 2001 Published by Elsevier Science Ltd.