Tin generates a wide variety of biological activities deriving from its chemical character. In this article, the biological activities of tin compounds are reviewed with a focus on the connection with immunity. The table of contents is as follows: Introduction, 1. Inorganic Tin and Immunity, 2. Organic Tin and Immunity, 2.1. Immunotoxicity, 2.1.1. Immunosuppression, 2.1.2. Thymus atrophy, 2.1.3. Changes in the membrane surface antigens of T cells, 2.2. Antitumor activity, 2.3. Anti-inflammatory action, 2.4. Tolerance manifestation of thymus atrophy, 3. Cellular and Biochemical Aspects of the Activity Manifestation, 3.1. Intracellular distribution of organotins 3.2. Effects on structure and function of Golgi apparatus and endoplasmic reticulum, 3.3. Effects on physical properties of phospholipid membrane, 3.4. Suppressive effects on cell proliferation system, 3.5. Consideration, Conclusion. To sum up this article, tin compounds (especially organotin compounds) act mainly on cellular immune systems and the mechanism appears to be due to their hydrophobicity-dependent intracellular distribution and their action on the phospholipid metabolism including the inhibition of intracellular phospholipid transport between organelles through an impairment of the structure and functions of the Golgi apparatus and the endoplasmic reticulum (ER), and the consequent inhibition of the membrane-mediated signal transduction system leading to DNA synthesis via phospholipid turnover and Ca2+ mobilization.