Abstract: Rice husk ash is the primary supplementary cementitious material, with rubber particles injected as artificial flaws. Rice husk ash and crumb rubbers engineered cementitious composites (CR-RHA/ECC) are low carbon, ecologically friendly cementitious composites with good ductility. The effects of rubber content (0, 10%, 20%, 30%) on the ductility and cracking characteristics of CR-RHA/ECC at each curing ages (7 days and 28 days) were explored employing macroscopic mechanical properties and microscopic investigations. The results show that: With the increase of age, there is a great difference in the ductility of CR-RHA/ECC. The replacement of 10% river sand by CR weakens the ductility of CR-RHA/ECC at 7 days by 54% and increases the ductility of CR-RHA/ECC at 28 days by 67%. With the increase of age (28 days), When CR replaces 30% river sand, the ductility of CR-RHA/ECC can reach 6%, and the tensile fracture width of CR-RHA/ECC decreases by 52.79% compared with that of CR-RHA/ECC without CR replacement.