Dispersed 1-tetradecyl-3-methylimidazolium chloride ([C14MIM]Cl) ionic liquid (IL) is insoluble with alkane solvents: 1-hexane, 1-octane, 1-decane, and 1-dodecane. Aggregation of IL, however, was initiated by adding 1-octanol (molar ratio of IL/octanol is 1/3), and rod-like single crystals grew after several days. Crystal growth was remarkably improved in the 1-octane solvent, which is expected to match with the alkyl chain lenght. The observed maximum crystal length was 5.2 mm. In addition, IL was not crystallized in an irregular shape solvent, 2-methyloctane. For further understanding of the crystallization conditions, we analyzed the components of the crystal by varying the IL/octanol ratio and characterized the structure by indexing the X-ray diffraction data in the 1-octane solvent. Increased 4 angstrom of the lattice parameter along the b-axis (normal to the imidazolium ring plane) distinguished itself against the triclinic structure of [C14MIM]Cl powder, and it well corresponded with the interspaced octanol molecule.