In this research, it was introduced a new and efficient nanocomposite that is composed of heteropolyacid stabilized on mesoporous titanium oxide and graphitic carbon nitride. The prepared nanocomposite was analyzed and characterized by XRD, FE-SEM, EDX, Mapping, Raman, TGA, TEM and BET techniques. An investigation of three-component condensation reaction of the aromatic aldehydes, 2-naphthol and urea was carried out by using H3PMo11O39@TiO2@g-C3N4 as nanocatalyst at 80 oC under solvent-free conditions. As a result of the synthesis of 1,3-oxazine derivatives, short reaction times (5-12 min), mild conditions, high product yields (85-95 %), purity, easy preparation, compatibility with the environment, low cost, chemical stability and high selectivity were obtained. Furthermore, it is easy to recover the prepared nanocomposites by filtration and they can be reused for at least five runs in the reaction without losing their catalytic activities.