In this paper was evaluated the influence of the different amounts and lengths of synthetic fibres on concrete´s mechanical properties. Polypropylene (PP) fibres were tested as reinforcement with two different lengths in concrete matrix. The specimens containing PP fibre have been showed better mechanical performance in comparison with samples with no fiber. Ratios of 0,5%, 1%, 1,5% and 2% of fiber was tested. Mechanical properties of samples have been improved by increasing content of fibres to maximum level and then decreases with higher number of fibres in matrix of concrete, although of samples containing fibres with unique and short length of fiber have a worse behaviour than majors’ and different lengths. This study is helpful towards the decision of optime quantity and length of fiber to incorporate in the matrix cement mortar.