Application of nanocomposite pour point depressants to improve the rheology of waxy crude oil is a novel and efficient technique and receives much attention. However, the effects of nano and microparticles alone on the rheology of waxy crude oil are unclear up to now. In this paper, monodispersed PMSQ microspheres with different sizes (200 nm-10 mm) were successfully synthesized through a two-step solgel route. Then the effect of the PMSQ microspheres on the flow behavior of two typical waxy crude oils was studied. The results showed that the PMSQ microspheres disperse well in oil phase as single spheres. A small dosage of the PMSQ microspheres significantly decreases the gelation point, elastic modulus G', viscous modulus G", apparent viscosity and yield stress of the two oil samples, indicating that the PMSQ microspheres improve the flow behavior of waxy crude oil at temperatures below the wax appearance temperature. The flow improving efficiency of the PMSQ microspheres is greatly influenced by the size and dosage of the microspheres. Moreover, adding PMSQ microspheres in the oil samples also inhibits asphaltenes precipitation because the PMSQ microspheres are capable of adsorbing part of the asphaltenes. However, the PMSQ microspheres have little influence on the exothermic character and microstructure of the two oil samples. Similar tests on a model waxy oil further confirmed that the PMSQ microspheres cannot participate in wax precipitation process and change the morphology of precipitated wax crystals, but can impede the interactions of the precipitated wax crystals through spacial hindrance effect, which inhibits the development of wax crystal network structure and thus improves the flow behavior of the oil. This mechanism brings a new way to improve the flow behavior of waxy crude oil and favors the development of new-generation flow improvers based on nano or microparticles. (C) 2017 Elsevier Ltd. All rights reserved.