Crystals of an aliphatic polyester, poly(tetramethylene succinate) (PBS) are investigated using transmission electron microscopy. Single crystals grown from a 0.01 wt % dichlorobenzene solution show a terrace-like morphology above 65 degrees C and a leaflike one at lower temperatures. The molecules are packed perpendicular to the basal plane of the single crystals, and twin crystals with a (110) twin plane are frequently observed. The thickness of the single crystal lamellae increases smoothly with increasing crystallization temperature. Lattice parameters of the PBS crystal in the monoclinic unit cell are determined from the electron diffraction patterns of the single crystals and stretched films as a = 0.523 nm, b = 0.908 nm, c = 1.079 nm, and beta = 123.87 degrees. The dimension of the c-axis is shorter than the value calculated from a fully extended chain conformation, as has already been found for other aliphatic polyesters. Two types of negative spherulites are observed according to growth temperature.