The present invention relates to a tube-fitting structure for a pure-water line of a water purifier or refrigerator. The present invention provides a tube connecting structure in which a tube fitted into a body having a fitting part formed therein is fixed by a cap, wherein a guide groove formed to have a receiving recess curved downward is formed on an outer circumferential surface of a tube link part of the body, and wherein a guide protrusion is formed on an inner circumferential surface of the tube corresponding to the outer circumferential surface of the body to allow the guide protrusion to be coupled along the guide groove, so that the tube is easily assembled with the body while the cap is rotated due to an inclined surface of the guide groove. Thus, in spite of enhancing the air tightness of the fitting structure, the assembly is improved.