Most countries in the world, led by Japan are recently burdened with a tremendous growth of elderly population. Unfortunately, to continue this trend is to guarantee the increase the number of age-related diseases such as infection or cancer in the very elderly, since our various biological functions are getting fragile and dysfunction with advancing age. Especially, immunological responses, such as susceptibility to infection or reduced response to vaccination linked to immunological memory, are also gradually impaired and reached in 'immunosenescence', although its defined molecular mechanism remains veiled. This article first summarizes the alterations in the quantity and quality such as numbers and functions as well as lymphocyte development and homeostasis in adaptive immunity, known to be primarily affected by immunosenescence. Continuously, another age-related alterations of innate immunity recognized as the first defense barrier with some inflammatory mediators and phagocytosis are also introduced.