The object of research is composite polymer reinforcement, specifically fiberglass rebar. This material has advantages over traditional rebar. Corrosion, for example, is the main problem of steel reinforcement, while composite rebar is resistant to it. Other merits and demerits of composite reinforcement are also considered. Monolithic concrete structures reinforced with composite rebars have increased durability because they are resistant to water or aggressive media. This is relevant, for example, for building foundations and monolithic structures of underground parking. It can be assumed that composite rebars are economically more beneficial than steel ones due to their physical and mechanical properties. The purpose of the study is to estimate the economic efficiency of using composite polymer reinforcement in the monolithic floor of the underground parking instead of steel reinforcement. Method. The research method used in the work is analytical calculation of the required quantity of both types of reinforcement for monolithic floor slab under given loads and their comparison. Results. It is determined that the replacement of steel reinforcement with FRP rebar reduces the cost of materials by 33%. Moreover, other factors that reduce costs at construction sites when composite reinforcement is used are also given.