Abstract: Piezoelectric nanomaterials have many unique properties, such as enhanced electromechanical coupling, low power dissipation and sensitive response, etc. Also such materials can meet the demand of microminiaturization of piezoelectric devices. These advantages make them strong candidates for applications in the fields of sensing, nanoelectromechanical systems (NEMS), flexible electronic device, and so on. As one of the most important features of nanomaterials, surface effect which resulted from the high ratio of surface to volume commonly plays a dominant role in the overall mechanical properties of piezoelectric nanomaterials. Due to the presence of surface effect, the bulk stress and bulk electric displacement jump across the piezoelectric surface, thus the classical continuity conditions are invalid. In this paper, the dispersion characteristics of SH guided waves propagating in a monolayer piezoelectric nanoplate are investigated with consideration of the surface effect. A surface is regarded as a two-dimensional continuum of zero thickness which possesses own material properties, and the influences of surface elasticity, surface piezoelectricity, surface permittivity and surface density are accounted into the non-classical boundary conditions of the piezoelectric nanoplate via the surface piezoelectricity model. The analytical expressions of dispersion relations are derived, and the numerical examples are provided to discuss the impacts of surface material parameters and nanoplate thickness on the symmetric and antisymmetric modes. Analysis results show that the propagation characteristics of SH guided waves exhibit obvious size-dependence. The surface effect has a significant impact on dispersion behaviors when the nanoplate thickness is small enough, while they may become more and more negligible as the thickness increases.