For membranes synthesized from crystalline polymers by phase inversion method, crystallization can sometimes dominate the precipitation process' to form a membrane characterized by the so-called particulate structure. Such is the case for PVDF membranes prepared by immersion-precipitation from water/triethylphosphate solutions. The structure of the membrane formed from this system was studied; in particular, the nano-scale fine structure of the crystallites, which form the matrix of the membrane. The phase diagram of the water/TEP/PVDF was determined using the cloud point method. Membranes were observed using LVSEM at low voltage (e.g., 1 KV) and high magnifications (e.g., 100 KX) to reveal the fine structure of the membranes.