A set of well-defined poly(ethylene-alt-propylene)-b-polylactide (PEP-PLA) diblock copolymers containing volume fractions of PLA (f(PLA)) ranging between 0.08 and 0.91 were synthesized by a combination of living anionic polymerization, catalytic hydrogenation, and controlled coordination-insertion ring-opening polymerization. The morphological behavior of these relatively low-molecular-A-eight PEP-PLA diblock copolymers was investigated with a combination of rheology, small-angle X-ray scattering, and differential scanning calorimetry. The ordered microstructures observed were lamellae (L), hexagonally packed cylinders (C), spheres (S), and gyroid (G), a bicontinous cubic morphology having laid space group symmetry. The G morphology existed in only a small region between the L-C morphologies in close proximity to the order-disorder transition (ODT). Transformations from L to G were observed upon heating in several samples. The efficacy of the reverse G to L transition in one sample was cooling rate dependent. The PEP-PLA Flory-Huggins interaction parameter as a function of temperature chi(PEP-PLA)(T) was estimated from T-ODT's by mean-field theory and subsequently used in the construction of the experimental PEP-PLA morphology diagram (chiN versus f(PLA)). The resultant morphology diagram was symmetric there were the well-defined L-C morphology boundaries. The low molecular weight of the materials imparted no significant deviation from previously documented diblock systems.