The paper presents the results of the study of the effect of micro silica on the strength of finegrained fiber concrete. The possibility of using micro silica as a partial replacement for Portland cement in the composition of fiber concrete has been studied. The cement replacement ratio was 5%, 10%, 20%, and 30% of the binder weight. A reference concrete mixture was also prepared. The authors performed tests to determine the setting time of cement dough with different percentages of micro silica. In the presented work micro silica, a complex additive based on polycarboxylate (MasterGlenium 27) and polypropylene fiber was used. Analysis of the results shows that such additives increase the compressive strength and flexural tensile strength depending on the dosage and change in the time of setting. The optimal composition of fiber concrete using micro silica and plasticizer based on polycarboxylate has been selected, which makes it possible to reduce cement consumption while improving the physical and mechanical characteristics of fiber concrete. It was shown that fiber concrete with the addition of micro silica together with plasticizer MasterGlenium 27 has high physical and mechanical properties.