Disclosed are an apparatus for preventing loosening and separation of a pinion plug of a steering assembly, and a rack and pinion type steering assembly comprising the same. An apparatus for preventing loosening and separation of a pinion plug in a rack and pinion type steering assembly, according to one embodiment of the present invention, comprises: a cylindrical pinion assembly part integrally provided on one side of a rack housing and having an opened upper portion formed with an internal thread on an inner circumferential surface thereof; a plurality of caulking grooves formed along the circumferential direction on an upper portion of the internal thread; a pinion plug having an external thread corresponding to the internal thread formed on the outer circumferential surface thereof so as to be screwed to the pinion assembly part, wherein a solid adhesive is applied to the external thread at a certain thickness; a caulking frame which is formed at an arbitrary height along the upper outer edge of the pinion plug on the external thread top, and which forms a stopper engaging with the caulking groove by plastic deformation of a part of the caulking edge toward the caulking groove after the threads are screwed, wherein the caulking groove is composed of a first direction groove on one side and a second direction groove on the other side with respect to an inflection point (I) which is the farthest from the center (C) of the pinion assembly part, and the inclination of the second direction groove is formed gently compared with the inclination of the first direction groove.