Mizaj (Temperament) forms the base of diagnosis and treatment in the Unani System of Medicine. Evaluation and classification of various temperaments are based on the intermixture of four akhlat (humours) in the blood in different proportions and thus blood plays an important role in the constitution of Mizaj. Domination of humours e.g., blood, phlegm, bile and black bile in the blood categorizes persons in sanguine, phlegmatic, choleric and melancholic temperaments respectively. Similarly, on the other hand, presence or absence of A and B antigens in the blood classifies persons into four groups, A, B, AB and O. This study was undertaken to find out the relationship between temperaments and blood groups of 120 healthy individuals.