Surface and interior lamellar assembly of dual-morphological spherulite generated from crystallization of poly(L-lactic acid) (PLLA) in the presence of atactic-poly(methyl methacrylate) (PMMA) have been characterized using polarized optical (POM), atomic forced (AFM), and scanning electron (SEM) microscopes. The formation of spherulite with dual morphologies takes place when the blend is crystallized at intermediate temperatures where the mobility of polymer chains is moderate, yet the crystallization rate is high. Besides the crystallization temperature, other factors such as molecular weight of both polymers, composition of the blends, as well as sample thickness have also been considered regarding their influence on the formation of dual-morphological spherulites (differ in their optical birefringence and lamellar arrangement). Direct observations toward the interior lamellar assembly have been conducted by fracturing the crystallized sample and subsequently etching out the amorphous portions from the spherulites. PLLA crystals are found arranging themselves into sheet-like and rod-like lamellae on the glass substrate. The development of these two distinct lamellar arrangements started from the nucleation site has been recorded. Each bundle of sheet-like lamellae at the nucleation site grows as one fibrous region as they cover a greater area; the area in between is covered by the rod-like lamellae growing to/from the substrate at a slower rate. Differ in their long axes and orders; both types of lamellae grow together composing a dual-morphological spherulite. This study demonstrates the microstructure instability induced by rapid crystallization of PLLA in a miscible blend with an amorphous polymer.