An object of the present invention is to provide a method of joining resin tubes, in which the degree of freedom of selecting a tube material is large, and further a defect such as stiffness and contraction at joining portions of the tubes is not developed. The method of joining resin tubes according to the present invention is a method of joining resin tubes so that a first tube is joined to a second tube, the first tube and the second tube each being made of synthetic resin, the method comprising: a surface activation step of activating each of a joining region of the first tube and a joining region of the second tube； and an adhesion step of adhering the joining region of the first tube obtained via the surface activation step with the joining region of the second tube obtained via the surface activation step to each other.
