Abstract: X-ray study, density measurement and estimation of aoousto-optic properties of the compounds in PbO-Nb₂O₅ system were carried out. Existence of the six PbO-NbaOs compounds reported by Roth was confirmed by X-ray analysis. Cell parameters and powder diffraction data were accurately measured for the compounds P₃N and P₅N₂. It was found that in the mixture of PbO and Nb₂O₅ with a composition of P₅N₂ heated at 900~1150℃ there exists P₃N as an intormediate phase. In this system the compounds P₃N, P₅N₂, P₂N and P₃N₂ with high PbO contents all possess large values of acousto-optio figures of merit and thus are promising new aoousto-optic materials.