PURPOSE: A plant growth promotor using crab shells and a manufacturing method thereof are provided to maximize the activity of microorganism which manufactures chitinase. CONSTITUTION: A plant growth promotor using crab shells is obtained by pulverizing the crab shell into the particle size of the diameter of 15-25 micro meters. A manufacturing method of plant growth substances using the crab shell comprises the following steps: removing crab part by using a centrifugation gradient technique from the crab shell and to remove foreign materials using a high pressure jet; drying the crab shell by using a false-twisting drying method; a first pulverizing the dried crab shell by using hammer mill; and secondarily pulverizing the crab shell into the average particle diameter of 20 micro meters using ACM(air classifier mill). The hammer mill pulverizes the crab shell into the particle size of 1-10mm. The ACM pulverizing device pulverizes the crab shell into the particle size of 15-25 micro meters.
