Hollow glass microspheres (HGMs) are ultra-lightweight materials and can be used as lightweight high-performance fillers. They are also environmental friendly because they contain 45 wt% recycled glass. In this study, the effect of HGM type and content on the mechanical behaviour and microstructure of ultra-lightweight engineered cementitious composites (ULW-ECCs) were investigated. 11 types of HGMs with different surface coatings, strength and density were used to replace fly ash at 60, 80 and 100 vol%. Compressive strength, flexural strength and flexural toughness were assessed, along with the modulus of elasticity and strain at peak stress. The effect of HGMs on the behaviour of ECC was also studied by microscopy. By using HGMs as lightweight fillers, a ULW-ECC with density less than 1400 kg/m3 was developed by replacing 100% fly ash with H40 type HGM. This newly developed ULW-ECC has a compressive strength above 30 MPa and a flexural strength of 14.4 MPa while maintaining the distinctive strain-hardening behaviour of ECC.