This book is going to discuss and debate on how to understand the Spinoza's Substance with reference to Descartes Substance. And along with I would interested to discuss on how Spinoza established his theory of substance which is how much different from his earlier philosophers. And then, I will focus on his idea of substance monism, which is key point of his metaphysics. Why he has given this single or mono substance? What made him to say that God is only and one substance? In my second chapter I will focus on his theory of attributes, for him there are infinite attributes, why he said like that? Is there any proofs for his claims? If yes, what are they? What is the exact notion of his God? What is the relation between mind and body? And how Spinoza relates attributes to the problem of mind body?