An oil drain preventing device for a continuously variable valve timing apparatus includes: an advance angle oil passage connected to a continuously variable valve timing (CVVT) journal from an an oil control valve (OCV) groove to which an oil control valve (OCV) is mounted to supply an oil supplied from a hydraulic pump to a continuously variable valve timing (CVVT) apparatus; a retard angle oil passage connected to the CVVT journal from the OCV groove; and a valve unit mounted to the advance angle oil passage and the retard angle oil passage between the oil control valve and the CVVT journal for preventing the oil supplied to the continuously variable valve timing apparatus from being drained by selectively opening/closing the advance angle oil passage and the retard angle oil passage according to a starting ON or a starting OFF of the engine.