The polarization of high-harmonics from aligned N(2) molecules was measured by observing the visibility of spatial interference between two high-harmonics generated separately. The minimum visibility was observed at an angle of 60 degrees between the polarization of the harmonic generation laser field and the molecular orientation. In this case, the angular shift of harmonic polarization is 15 degrees from the molecular orientation. Our measurement of the visibility variation matches the theoretical prediction based on the harmonic field calculation for aligned N(2) molecules.