In this paper, several types of binary nanofluids were prepared by mixing TiN, SiC, carbon black nanoparticles with emulsifier OP-10, and Al2O3 nanoparticles with sodium dodecyl benzene sulfonate (SDBS), to ammonia-water solution, respectively. The influences of ammonia, nanoparticles, and surfactant on the surface tension of the binary nanofluids are investigated by using a QBZY-1 digital surface tensiometer. The results show that the surface tensions of ammonia water decrease approximately linearly with the increase of ammonia content. For the nanofluid (TiN, SiC) without surfactant, the nanoparticles can softly reduce the surface tension of the binary nanofluids. While for the nanofluid (Al2O3, carbon black) containning surfactant, the existences of surfactant greatly reduce the surface tension of the binary nanofluids. When the content of surfactant is lower than critical micelle concentration(CMC), adding nanoparticles can increase the surface tension of the fluids, which may be caused by the decrease of the “free” surfactant content induced by the adsorption of surfactant on the surface of nanoparticles.