A method of preparing ZSM-5, comprising: preparing nanocrystalline ZSM-5 seeds by using a composition represented by [TPA+] 25 [SiO 2] 100 [Al 2 O 3] x [H 2 O] 1600 where X is 0.5-10, wherein the composition is stirred, aged at room temperature and crystallized, wherein the nanocrystalline ZSM-5 seeds obtained have a relative crystallinity of 100% or more, which is evaluated by X-ray diffraction analysis, and have a size of 70 - 300 nm as measured by SEM; adding the nanocrystalline ZSM-5 seeds to a solution including water glass as a silica source, an alumina source, a neutralizer and water to form a reaction mixture, wherein the preparation of the reaction mixture comprises the following steps: - a silica source and water are mixed and then stirred for 20 - 40 minutes to form a first aqueous solution, - an alumina source, a neutralizer and water are mixed and then stirred for 15 - 30 minutes, and then the synthesized nanocrystalline ZSM-5 seeds are added thereto to form a second aqueous solution, - the first aqueous solution and the second aqueous solution are mixed with each other to prepare the reaction mixture stock solution, wherein the amount of seeds added to the solution is 0.1 to 6 wt% based on the reaction mixture and wherein the reaction mixture stock solution has a composition represented by [Na 2 O] X [Al 2 0 3] Y [SiO 2] 100 [H 2 0] Z in which X is 10 - 26 moles, Y is 0.2 - 5 moles, and Z is 2500 - 4000 moles, wherein the alumina source is selected from sodium aluminate, aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum acetate, aluminum isopropoxide, aluminum acetylacetonate, and mixtures thereof; and maintaining the reaction mixture at 150 - 200°C to crystallize the reaction mixture, wherein the crystallizing of the reaction mixture is performed for 12 - 48 hours, wherein the ZSM-5 is prepared in the absence of an organic structure-directing agent, and the ZSM-5 has a narrow particle size distribution such that its average particle size is controlled within the range of 0.2 to 2.0 μm measured by SEM, and no phase impurities is obtained and wherein the neutralizer is any one selected from hydrochloric acid, nitric acid, sulfuric acid. preparing nanocrystalline ZSM-5 seeds by using a composition represented by [TPA+] 25 [SiO 2] 100 [Al 2 O 3] x [H 2 O] 1600 where X is 0.5-10, wherein the composition is stirred, aged at room temperature and crystallized, wherein the nanocrystalline ZSM-5 seeds obtained have a relative crystallinity of 100% or more, which is evaluated by X-ray diffraction analysis, and have a size of 70 - 300 nm as measured by SEM; adding the nanocrystalline ZSM-5 seeds to a solution including water glass as a silica source, an alumina source, a neutralizer and water to form a reaction mixture, wherein the preparation of the reaction mixture comprises the following steps: - a silica source and water are mixed and then stirred for 20 - 40 minutes to form a first aqueous solution, - an alumina source, a neutralizer and water are mixed and then stirred for 15 - 30 minutes, and then the synthesized nanocrystalline ZSM-5 seeds are added thereto to form a second aqueous solution, - the first aqueous solution and the second aqueous solution are mixed with each other to prepare the reaction mixture stock solution, - a silica source and water are mixed and then stirred for 20 - 40 minutes to form a first aqueous solution, - an alumina source, a neutralizer and water are mixed and then stirred for 15 - 30 minutes, and then the synthesized nanocrystalline ZSM-5 seeds are added thereto to form a second aqueous solution, - the first aqueous solution and the second aqueous solution are mixed with each other to prepare the reaction mixture stock solution,