Provided is an ethyleneimine polymer which exhibits excellent close adhesion properties and adhesive properties and is unlikely to form a gel-like film, and a method for producing the same. An ethyleneimine polymer, wherein a number average molecular weight (Mn) of the ethyleneimine polymer measured by gel permeation chromatography in terms of pullulan is 13,000 or more, a degree of dispersion of the ethyleneimine polymer is greater than 3.0 and 5.0 or less, and a water content in the ethyleneimine polymer is from 3 to 35% by weight.