Nonstoichiometric barium ortho aluminate with the general formula Ba1-xAl2O4-x (0 < x < 0.56) was synthesized by the thermal decomposition of barium aluminium oxyhydroxide prepared through gel-to-crystallite conversion method. Phase singularity was confirmed by x-ray powder diffraction. The large range of nonstoichiometry is explained in terms of Ba2+ vacancies within the corner sharing A1O(4) network, whereby the nepheline structure extends into the "stuffed" tridymite lattice. HREM studies indicated the ordering of point defects leading to the formation of extended defects and stacking faults. The coordination of aluminium remained tetrahedral as revealed by Al-27 MAS NMR. On doping with Eu(II), Ba1-x-yEuyAl2O4-x+y (0.005 < y < 0.05) shows the emission maximum around 500nm, the intensity of which increases with the x-value.