The article deals with the degradation of cement beams containing polypropylene and polyvinyl alcohol fibres. Nowadays it is developed high-quality concrete that contains a minimum of reinforcement or all it is replace by micro fibres. Microscopic examination of fiber breakage and changes at fiber-matrix interface was investigated in this paper. The cement beams were stored in an aggressive environment of 3% NaCl, 5% NaOH and 5% H2SO4 for 28 days (CSN P CEN / TS 12390-11). Mechanical parameters and changes of fibres structure was monitored after 7 and 28 days. The confocal laser scanning microscope Lext OLS 3000 with 3D display capability was used to monitor degradation changes. Aggressive environment represent by chloride solution (NaCl) and sulphate solution (H2SO4) was simulated within the resistance test. On the basis of the measured experiments, it can be concluded that, aggressive environment had just negligible influence on the mechanical parameters and the degradation of the individual fibres did not show at all.