A wick sheet for a vapor chamber is sandwiched between a first sheet and a second sheet of the vapor chamber that encloses a working fluid. The wick sheet for a vapor chamber includes a sheet body having a first body surface and a second body surface, a penetration space that penetrates the sheet body, a first groove assembly that is disposed on the second body surface and that communicates with the penetration space, and the second groove assembly that is disposed on the first body surface and that communicates with the penetration space. The flow channel cross-sectional area of a second mainstream groove of the second groove assembly is greater than the flow channel cross-sectional area of a first mainstream groove of the first groove assembly.