A vapor chamber and an assembly method thereof are provided. The vapor chamber includes a mesh structure including a main body and an extension part. The main body and the extension part have a capillary-wick structure, respectively. The extension part is extended outwardly from a side of the main body and folded along an intersection between the extension part and the main body. The extension part is stacked on the main body. An overlapping area is formed by stacking the extension part on the main body, and the overlapping area fails to contact with a support structure. The main body is disposed on a first concave of the lower case. The upper case covers the lower case and is assembled with the lower case. A second concave of the upper case and the first concave collaboratively form a space. The mesh structure is accommodated within the space.