Ecological Marxists argue that Marx forged a view of nature compatible with more recent models of environmentalism. John Bellamy Foster argues that Marx ascribed an ecological value to nature by asserting a co-evolution between man and nature. James O’Connor presents a more nuanced view in which Marx at best defended a conservationist defense of nature. I argue that such ecological views of Marx tend to overlook his abandonment of an ontology of nature as a totality of relations among physical objects with respect to their interactions and mutual preservation and order. He followed Kant in reducing nature, or the physical world, effectively to a regulative notion, thus reducing its value to a simply a heuristic one for judgments about and actions towards objects. But he also radicalized this reduction by envisaging nature only as a material field of fungible and consumable things, such that each thing is a mere locus of energy or force that human labor cannot substantively perfect but only change to a function. Labor in this view creates new arrangements of natural things for a singular ultimate purpose: the formation of associations of free labor. I conclude that Marx’s thinking thus cannot be utilized to support an environmental philosophy, such as deep ecology or eco-socialism, that would posit any intrinsic value to nature.