Seed oil bodies are lipid storage organelles that comprise a triacylglycerol matrix surrounded by a monolayer of phospholipids embedded with proteins. The oil-body associated proteins include the abundant structural protein, oleosin and at least three minor proteins. Recently, genes encoding two of the three minor proteins were cloned from maturing sesame seeds. Both sequence analyses and biochemical studies indicate that these two minor proteins are calcium-binding and sterol-binding proteins, and thus named caleosin and steroleosin, respectively. Here we review the structure- function relationship of these three oil-body proteins and their targeting to oil bodies during seed maturation.