Additive manufacturing (AM) is a digital manufacturing technique within the Industry 4.0 paradigm, which found its applications in various sectors. Despite the significant development undergone in the recent years, it still requires more insight into the microscopic and macroscopic aspects of manufacturing processes as well as systems. Fused deposition modelling (FDM) has become one of the most important AM technology due to its capability to produce functional prototypes with complex shape compliant with industrial applications in a cost effective way. The process is usually adopted for fabricating components in a variety of polymers for testing prototypes both functional and aesthetic. The mechanical behaviour of specimens fabricated using FDM machine has been studied presented in several works. However, they are focused mainly on ABS, while very few papers analysed the mechanical properties of FDM samples made of PLA filament. Even though ABS has superior mechanical properties, some application might require the use of PLA, which offers several advantages, so that a deeper investigation on its properties is needed. Therefore, in this study, the influence of the main FDM process parameters on mechanical performance of PLA samples has been evaluated. The aim of the work is the analysis of the effects of the process parameters and the development of a prediction model in order for the designers to fulfil the specifications of the final product. The mechanical tests have been carried out on miniaturized standard ISO-527 tensile specimens focussing on the tensile test main properties: ultimate tensile stress, Young’s modulus and elongation at break. Moreover, an equivalent experimental campaign has been carried out using PLA with carbon fibre filaments, in order to evaluate the effects of the reinforcing filler and the process parameters on the mechanical properties of the specimens.