This paper presents a study on the effects of particle size for pendant drop surface tension of nanofluids. The main purpose is to conduct an analysis of nanofluid on this interfacial property. First, water-based nanofluids are prepared. Then, the secant method is used to solve the nonlinear differential equation so as to predict the pendant drop profile. Finally, by comparing with numerical predictions and experimental observations, the analysis on surface tension of nanofluids is completed. The experiment results reveal that a nanofluid with smaller particle size can benefit a smoother variation of the surface tension with the particle volume fraction and this effect can be further magnified by increasing the magnetic interaction.