The percentages, lengths and diameters of chopped basalt fiber in concrete mixture have high influence on concrete strength. On the other hand, expanded clay contributes mostly in the weight reduction of the concrete hereby, giving what is called lightweight concrete. The collapse of concrete structures can be blamed to the effect of cracks that are born in the weak concrete structures. This paper shows how expanded clay with chopped basalt fiber of length 20mm, diameter 1.5μm affected the maximum load that the concrete samples bear and how the existence expanded clay and basalt fibers affect the concrete in terms of resistance to cracks seen through the bending (flexural) and strength on compressive of the concrete samples. The purpose of this research paper is to investigate the effect of chopped basalt fiber with expanded clay in strengthening the mechanical behaviour of concrete. Concrete specimens were mixed with chopped basalt fiber and casted, the strength checked on 7th, 14th and 28th day and evaluated based on flexural strength, compression strength. The addition of basalt fiber in the specimens showed significant effect where the compressive strength decreased while the flexural strength increased. © 2019 IOP Publishing Ltd. All rights reserved.