The strength and fracture properties of epoxy resin modified cement mortar are studied. The amount of epoxy resin added varies from 5% to 17% by weight. Compared to the control unmodified cement samples, the experimental results show a 65% increase in flexural strength and a 85% increase in the specific fracture work at about 10% epoxy content. It is verified that void-filling is not the strengthening mechanism involved. The maximum size pores are less than the calculated size of the critical flaw so that they do not control the flexural strengths of these epoxy resin modified cement mortars. This finding is consistent with the concept of the crack growth resistance curve applied to cement mortar.