Developing and commercialising successful products is crucial if a firm is to gain a lasting competitive edge. It is widely held that organisational culture is a key determinant of new products success. Some studies suggest that culture has a positive effect on the proficiency with which firms develop new product process, and that is what explains its influence on new product success. However, empirical research on the mediating role of new product process proficiency in the relationship between organisational culture and new product success is very scarce. This paper examines this mediating role, and tests it using a sample of 253 Spanish firms and applying Structural equations modelling. Findings provide support to that hypothesis in the case of adhocracy and market cultures, and show that adhocracy, in addition, has a direct effect on new product process proficiency. However, contrary to our expectations no significant results were obtained for clan and hierarchy cultures.