The present invention relates to a method of manufacturing ultra-low viscosity hydroxyalkyl cellulose through a partial neutralization method, and the method includes: reacting cellulose with an alkalizing agent to obtain alkalized cellulose; reacting the alkalized cellulose with an etherifying agent to obtain hydroxyalkyl cellulose; performing first neutralization of the hydroxyalkyl cellulose; decomposing the hydroxyalkyl cellulose by using hydrogen peroxide; and performing second neutralization of the hydroxyalkyl cellulose. Through the aforementioned method, ultra-low viscosity hydroxyalkyl cellulose can be manufactured while preventing a process problem, such as swelling, which may occur through the decomposition of an acid treatment.