Langasite (La3Ga5SiO14 or abbreviated as LGS) single crystal is an attractive substrate for surface acoustic wave (SAW) devices requiring good temperature stability and higher electromechanical coupling constant than quartz. AlN thin films are attractive materials that have some excellent characteristics, such as high SAW velocity, piezoelectricity, high-temperature stability, and stable chemical properties. In this study, AlN thin films were deposited on LGS to be a new composite SAW substrate (AlN/LGS) by reactive RF magnetron sputtering method. SAW delay-line device was manufactured on this substrate. The performance of the device was measured by network analyzer (Agilent 8753E).The results exhibited the composite substrate (AlN/LGS) increased the Rayleigh wave velocity, decreased the insertion loss of SAW devices, and suppressed the harmonic response.