Crab waste (Portunus pelagicus) has the potential to become a more valuable product, namely chitin and chitosan. Chitosan as a plant growth promoter is a natural compound that is biodegradable and non-toxic. Chitosan which is used as liquid organic fertilizer functions as a growth promoter, due to the provision of amino compounds, which can stimulate the initial growth stage. The purpose of this study was to use crab waste (Portunus pelagicus) to isolate and characterize chitosan, then use chitosan as liquid organic fertilizer. Characterization of the FTIR spectrum of chitosan isolated from crab, showing the absorption value of the hydroxyl/amine group (OH-, NH2-) shown at the peak of 3435.54 is 92.17% while the absorption value of the amide/acetamide group (CH3CONH-) at the peak is 1654.67 is 91.16%. And obtained the deacetylation degree of chitosan from crabs ranging from 40.25-79.35%. The use of Liquid Organic Fertilizer-Chitosan as a growth promoter has a significant effect on increasing mass, height, root length, and number of Dayak Onion leaves. Where the optimum concentration of Liquid Organic Fertilizer-Chitosan for Bawang Dayak is 60% (v/v).