The object of research is the dispersed reinforcement with polypropylene fiber of expanded clay concrete produced by using local raw materials. The purpose of this study is to select the optimal reinforcement ratio of expanded clay concrete containing polypropylene fiber. It is also proposed to investigate which variation of adding fiber is most effective (as an admixture with a constant content of the binding material or instead of cement mass). Method. Polymer fiber reinforcement should be added to the dry mix, thoroughly mix all the components and only then add water to the mix. In case of non-observance of this condition, it is impossible to achieve a homogeneous distribution of fiber in the hardened concrete, and therefore, the effect of disperse reinforcement will be reduced to zero. Results. As a result of investigations, special attention must be paid to the correct preparation technology at the time of concrete mixture preparation. Otherwise, the polymer fiber introduction will have a negative effect. In this case, the coarse aggregate use is a significant condition. The secant modulus of elasticity will decrease by more than two times if the diameter of expanded clay grains increases. It is recommended to use expanded clay gravel with smaller fractions in accordance with investigations. The maximum and minimum allowable content of polypropylene fiber are 0.5–1.5 %. The compressive cube strength increase of expanded clay concrete by polypropylene fiber is achieved by this allowable content in comparison with unreinforced expanded clay concrete with a similar concrete mixture. The most effective is reinforcement ratio of 1.5 %, and the maximum compressive strength increase by 14 %. The polypropylene fiber should be added in a percentage ratio depending on the cement mass with constant cement content in accordance with investigations. The fiber introduction instead of cement by mass negatively affects the strength characteristics.