Disclosed herein is a liquid pharmaceutical composition of botulinum toxin which is improved in stability. It comprises botulinum toxin, polysorbate 20, and methionine and optionally isoleucine. Employing, instead of the animal-derived protein albumin or gelatin, a combination of polysorbate 20 and methionine and optionally isoleucine as botulinum toxin stabilizers, the liquid pharmaceutical composition eliminates the risk of contaminating the body with serum-derived pathogens or microorganisms and can be administered safely to the body. Also, the composition is convenient for use as a direct injection for patients. Superior to conventional compositions employing either detergents or amino acids in terms of the storage stability of botulinum toxin at 25˜370C as well as at refrigerated temperatures, the liquid pharmaceutical composition of the present invention is very useful for storing botulinum toxin under an emergency condition such as an environment without maintaining low temperature. The liquid pharmaceutical composition can be readily prepared because it employs a detergent and an amino acid(s) without a lyophilization process.