Abstract: The present invention relates to a method for producing botulinum toxin in various fragments to then be reassembled, for safely producing same. In the present invention, devised is a method in which: botulinum toxin is produced in fragments by cleaving light and heavy chains thereof into two or three pieces, respectively, and then combined as a full-length toxin, thereby allowing high complexity in production, due to toxicity, as well as low safety and economic feasibility, to be overcome; production of water-soluble botulinum toxin is enabled by using bacteria, thereby markedly shortening the production time as compared to existing production methods; and conjugation of the produced fragments with other proteins and nanoparticles is also enabled, thereby increasing the pharmaceutical extensibility of the toxin.