Abstract: Under extreme disasters such as earthquakes, aging masonry structures are highly vulnerable to out-of-plane failures and damage, which can even result in the collapse of the building. To address this issue, this study investigated the out-of-plane mechanical properties of masonry structures reinforced with Engineered Cementitious Composite (ECC). Six reinforced specimens with different ECC overlay thicknesses were designed and fabricated, and three-point or four-point bending static tests of the specimens were carried out. The test results showed that: different from the brittle failure of ordinary masonry, ECC-reinforced masonry presented a ductile flexural or flexural-shear failure mode; ECC can alleviate localized a stress concentration in the masonry, and effectively limit the rapid development of larger cracks; and the reinforcement of ECC can improve both the load carrying capacity and the deformation capacity. When the thickness of the ECC layer in tension was increased from 10 mm to 30 mm, the peak load of the specimen was increased by up to 183%, and the ultimate deflection ratio of the specimen was increased by up to 107% by further increasing the thickness of the layer in the compression zone to 30 mm. The numerical model of ECC-reinforced masonry was established, and the precision of the model was verified by comparing with the test results. The comparison results indicated that the numerical model can not only reflect the damage pattern of the test specimen well, but also accurately predict the mechanical properties of the specimens, in which the deviation of the peak load prediction is not more than 10%. A broader parametric analysis was conducted with this numerical model. Based on the equivalent method of bending performance analysis, it is recommended that when seismic strengthening is carried out for masonry with a fortification intensity of 8 degrees and below, at least 20 mm thick ECC layers are suggested for double-sided strengthening; and that when the fortification intensity is 9 degrees, the thickness of the layers is recommended to be higher than 30 mm. This study provides a reference for the overall strengthening of masonry buildings.