The present invention relates to a pipe connection assembly of a heat exchanger for connecting a header tank and a pipe of the heat exchanger, in which a means for preventing a welding ring that fixes a manifold and a pipe from entering into a hollow at one end of the manifold before welding is disposed, and a space is formed between the inner surface of the one end of the manifold and the outer surface of the pipe, thereby preventing the molten welding ring from flowing out.