We developed a route to synthesize rutile TiO2 nanocrystals (NCs) with the assistance of 1-butyl-3-methylimidazolium chloride (bmim(+)Cl(-)). The phase transformation from anatase to rutile phase was investigated, and a simple model to describe the phase transformation process was proposed considering that the nucleation and growth of rutile phase were determined by the aggregation manner of anatase NCs and Ostwald ripening process, respectively. It was demonstrated that the surfactant-like nature of the IL used was crucial for controlling the crystallization process via controlling the aggregation manner of the NCs. The phase, shape, and size of TiO2 NCs could be tuned by the controlling the operating conditions, such as temperature, solution acidity, and reactant concentration of the bmim(+)Cl(-)/TiCl4/H2O reaction system. Phase-pure rutile multipods and 1D nanorods with different sizes were controllably obtained.