An LED lamp includes a transparent sheet, a grid casing, a printed circuit board (PCB), liquid sealant, and a lid. The transparent sheet covers on a top of the grid casing. The PCB is located between the grid casing and the lid. The grid casing has a surrounding portion and a grille portion. The lid covers a bottom of the grille portion and secures the PCB. A sealed room is formed in the grille portion and enclosed by the transparent sheet, the grid casing and the lid. The surrounding portion has a feeding channel communicating with the grille portion. The liquid sealant is fed into the sealed room through the feeding channel. The feeding channel is finally closed to seal the liquid sealant.