In this study, the seismic behaviour of G+3 building consisting of frame structure made with Glass Fiber Reinforced Polymers (GFRP) and infilled with Sustainable Engineered Cementitious Composite (ECC) was investigated numerically. In order to reduce the usage of cement in ECC, it was replaced with 80% Fly Ash which in turn will result in the reduction of Carbon footprint. The mechanical properties of GFRP and ECC were carried out using direct tensile strength and three point loading test. The G+3 structure was modelled and analysed using Robot Structures software. The Natural Frequency, Mode shapes and Lateral Displacement of the building were investigated. The results were also compared with the conventional Reinforced cement Concrete (RCC) Structure. The lateral displacement of GFRP sections infilled with HVFA-ECC is higher than RCC structure and fundamental Frequency of RCC structure is higher than GFRP sections infilled with HVFA-ECC. © 2021 Alpha Publishers. All rights reserved.