To compensate for the deficiency of natural sand (NS) resources during the production of selfconsolidating mortar (SCM) in the area with limited medium sand resources and promote the utilization of ultra-fine sand (UFS), this study aimed to use UFS as a substitution of medium-size sand in the production of selfconsolidating mortar (SCM) and examine the effect of different replacement ratio on the rheology of self-consolidating mortar (SCM). The results showed that there existed an critical UFS replacement ratio with regard to its influence on the rheology properties of the SCM. This is because the high water absorption capability of UFS can decrease the free water content in the SCM matrix, resulting in the deterioration of its rheological properties. However, the particle ef? fect of the UFS could improve the gradation of self-compacting mortar, allowing more free water to be released dur? ing mixing and improving the rheological properties. The viscosity and the yield stress of the SCM mixture increased as the UFS ratio increased. Also, the influence of the high water absorption of UFS on consistency was more obvious at UFS replacement ratio over 30%. Taken together, the UFS ratio should be fixed within 30% for the production of SCM with a good rheological performance.