This article describes the fuzzy classification system developed by the authors and that is particularly applicable to bioinformatics data classification. The description focuses on the following steps in the system: 1) Data preprocessing; 2) Classifier training and construction of the rule base; 3) Classification of new records and 4) Evaluation of the results; it also explains the details of processes in each step as well as the processes of missing data replacement, reduction of the number of alternatives and functions, construction of membership functions and stretching of the induced rules. The article concludes with a justification of the methods and algorithms chosen for each process of the system.