Mizaj (temperament) is one of the fundamental concepts of Unani system of medicine. Internal and external factors influences the human body leading to altered temperament that ultimately inflict the whole body or a specific organ in the form of disease. Therefore, mizaj of a patient or organ has to be evaluated. The principle of management of disease is to correct the altered temperament. If it is disturbed, body becomes more susceptible to develop such diseases having same temperament as that of an individual. Evaluation and classification of various temperaments are based on the intermixture of four humours in the blood in different proportions and thus blood plays an important role in the constitution of Temperament. Domination of humours e.g., blood, phlegm, bile and black bile in the blood categorizes persons in sanguine, phlegmatic, choleric and melancholic temperaments respectively.