This work deals with a utilization of a plasma treatment of polymeric macro-fibers used as reinforcement in the cement composites. Commercial fibers BeneSteel were plasma treated to reduce their weaknesses – smooth and chemically inert surfaces and thus to enhance an interfacial shear strength between them and the cement matrix. The low-pressure cold oxygen plasma treatment was done for both physical (roughening) and chemical (surface activation via active polar groups) surface modifications. A plasma exposition time differed between 5 and 480 seconds, while the surface changes were observed. It was shown that the most effective treatment time was equal to 30 seconds, as proven by a wettability measurement between fibers and demineralised water. To determine the interfacial shear strength between reference and chosen modified fibers, pull out tests from the cement matrix was performed. Finally, thus treated fibers were used as the reinforcement in concrete composites. Concrete samples having dimension equal to 100 × 100 × 400 mm were tested in the three-point bending test. We focused especially on the post-cracking response of tested samples. The results showed that the post-cracking residual flexural strength of samples reinforced with plasma treated fibers was higher by 30 %. It was find out that the utilization of plasma treated fibers is more effective if compared to reference ones. Copyright © 2017 VBRI Press.