GFRP bar has superior properties such as high corrosion resistance, high tensile strength, many times lighter than steel. Corrosion properties of traditional reinforcement due to the impact of the surrounding environment seriously affect the quality as well as the life of the structure. Therefore, GFRP bars are very suitable for replacing steel reinforcement in concrete structures that require the above special requirements, contributing to increasing the life of the work. This paper presents experimental results on instantaneous deflection of flexural members including: two GFRP reinforced concrete beams and a reference reinforced concrete beam; two reinforced concrete slabs GFRP and reinforced concrete slabs control. The results show that the deflection of GFRP reinforced concrete members is larger than that of reinforced concrete members. In addition, the content of longitudinal reinforcement and concrete strength also affect the deflection of the structure.