Morphology control of poly(p-phenylene pyromelliteimide) (PPPI) crystals was examined using reaction-induced crystallization of oligomers during solution polymerization of self-polymerizable N-(4′-aminophenyl)-3-carboxyl-4-alkoxycarbonylphthalimide. Micro-flowers of the PPPI needle-like crystals were formed in which the needle-like crystals grew radially from the center part as petals. The molecules aligned regularly along the long axis of the needle-like crystal. The structure of alkoxy group in the monomer and the monomer concentration influenced the size of the needle-like crystals, and their average length and width were changeable from 640nm to 1.69μm and from 110nm to 210nm, respectively. The average thickness was 20nm. The obtained micro-flowers possessed high crystallinity and exhibited excellent thermal stability.