The knowledge of microbiological and biochemical reactions in cheese can help to introduce process modifications necessary to improve the quality of products, without any loss in its characteristics. The aims of the present study were to investigate the changes in levels of the main microbial groups and in the physicochemical characteristics throughout the ripening process of Serrano cheese and the influence of the season of the year over these interactions. It is expected that this study will contribute to the establishment of microbiological quality standards for Serrano cheese, as well as to provide further scientific basis for the understanding of ripening process, which is necessary to improve farmhouse procedures.