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Epoxy adhesives for concrete cracks repair may necessitate the addition of reactive diluent to decrease their viscosity. However, research on the effect of different reactive diluents on the various properties of epoxy adhesives remains insufficient. In this paper, three reactive diluents, including monofunctional alkyl C12–C14 glycidyl ether (AGE), butyl glycidyl ether (BGE) and difunctional 1,4-butanediol diglycidyl ether (BDDE) are utilized to comparatively study the different effects on the viscosity, exothermic temperature, mechanical properties, and bond strength with cement mortar of the adhesives. The results show that the addition of BDDE increases the maximum curing temperature of the adhesives, whereas AGE and BGE both causes a decrease. The epoxy adhesive with AGE or BGE shows greater ultimate tensile strain, but a more obvious reduction in Young's modulus than that with BDDE at the same concentration. BDDE improves the bond strength of the adhesive-mortar interface whereas AGE and BGE both decrease it. Moreover, the bond strength shows a positive correlation with the hydroxyl content on the surface of cured epoxy. Comparing with AGE and BGE, BDDE increases the hydroxyl content, resulting in the strongest bond strength. [ABSTRACT FROM AUTHOR]