Epitaxial crystallization on the (001) substrate face of NaCl and KI of a perfectly alternating ethylene-carbon monoxide copolymer (poly(3-oxotrimethylene); POK) from its nitrobenzene solution has been successfully achieved. Transmission electron microscopy observations reveal that (a) the resulting crystal modification and orientation depend on the substrate and (b) POK chain stems in the rodlike crystals are parallel to the substrate surface and perpendicular to the long axis of the rod (namely, the edge-on folded-chain lamella). For the edge-on lamellae grown on KI, lattice images were successfully obtained in which (110) lattice fringes could be clearly identified. The length of the lattice fringes, viz., the stem length or crystalline core thickness, is estimated at about 60% of the total thickness of one epitaxially grown POK lamella.