This article focus to Define and Discuss on Cost Behavior in accounting perception. How a specific cost acts to changes in activity levels is known as cost behavior. Costs may stay the same or may change proportionately in response to a change in action. Knowing how a cost reacts into a change in the degree of activity makes it easier to manufacture a budget, prepare a forecast and determine which of two alternatives ought to be selected. Here briefly discuss on Fixed costs, Variable costs and Mixed costs. Finally analysis Scatter diagram, High‐low method and Least‐squares regression analysis.