System to urinalysis using FT-IR instruments is presented based on fuzzy logic knowledge. Linguistic expressions of the possibility of infection and the importance were quantified and membership functions were determined based on general quantitative criteria. Diseases considered were Diabetes Mellitus, Proteinuria, Microalbuminuria. Glucose, Protein, Albumin, Creatinine in 30 samples were analyzed by the present system, which resulted in 74% accuracy. The simple mathematical formulation of present system would enable an easy implementation in commercial analysis instruments. Also, the identical fuzzy logic can be applied to similar diagnostic environments in general.