We evaluated the effect of dilution on both the size and packing density of aggregates prepared from a fatty acid (oleic acid, OA)/detergent (3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxypropane sulfonate (CHAPSO)) bicelle as a parent for functional membrane materials. The sizes of the aggregates formed at different molar ratios, XOA(= [OA]/([OA]+[CHAPSO])), of 0.3 and 0.7 and their parent bicelles were measured by dynamic light scattering and transmission electron microscopy; their packing density was evaluated by deconvolution of the fluorescence spectrum, where Laurdan molecules were used as a probe. The experimental results showed that the bicelles formed aggregates upon dilution because of the hydration of CHAPSO. The packing density of the nano-ordered aggregate formed at XOA = 0.3 was much greater than that of the aggregate formed at XOA = 0.7, implying the formation of an ordered aggregate under the condition of XOA = 0.3.