In this paper, I look into the scholastic background of Descartes’s physics, and try to make it clear where his theory of causation stands when viewed in relation to the tradition of the scholastic theory of causation. In section 1, I give an outline of the scholastic theory of causation based on Disputationes Metaphysicae (1597), written by Francisco Suarez (1548-1617), a leading figure of the early modern Spanish scholasticism. In the middle ages, there were three rival views on the relationship between God and created things as efficient causes. They are occasionalism held by Islamic theologians, and concurrentism and conservationism held by scholastic Aristotelians. Occasionalism denies created thigs efficient causation and admits God as the only true cause. By contrast, both concurrentism and conservationism allow causation not only to God but also to created things. Conservationism differs from concurrentism in that the former does not hold, as the latter does, that God concurs with created things when they operate as efficient causes, and restricts the actions of God as an efficient cause to the creation of things and the conservation of the things created. In section 2, I give a brief account of Descartes’s physics based mainly on Principia Philosophiae (1644), and take up the issue whether his theory of causation is to be interpreted as occasionalism, concurrentism, or conservationism. Scholastic Aristotelians made a distinction between God, which is the primary, universal cause, and created things, which are particular, secondary causes. Descartes also holds that God is the universal, primary cause. But it is the laws of nature and not created things that he regards as particular, secondary causes. Paying attention to this characterization of laws as particular, secondary causes, and its position between God and created things, I argue that Descartes, though retaining an element of cocurrentism or conservationism, advances toward occasionalism, which is going to be held by his followers such as Nicolas Malebranche.