Disclosed is a method of fabricating an optical fiber preform using a modified chemical vapor deposition method and a nonlinear optical fiber fabricated using the method, in which an impurity component is doped after both ends of a quartz glass tube are partially collapsed, so that an impurity doping process can be stably executed and the doped quantity of the impurity component can be increased. The method comprises the steps of: forming a cladding layer and a core layer in a quartz glass tube; partially sintering the core layer; partially shrinking both ends of the quartz glass tube, in which the cladding layer and the core layer partially sintered are formed; and doping a sintered portion of the core layer with an impurity component, so that the optical fiber preform fabricated has a predetermined function. The nonlinear optical fiber comprises a cladding layer and a core layer, the nonlinear optical fiber being fabricated by a process comprising the steps of: forming the cladding layer and the core layer in a quartz glass tube; partially sintering the core layer; partially collapsing both ends of the quartz glass tube; and doping a sintered portion of the core layer with a predetermined impurity component.