A wire harness waterproof structure is provided that allows the water sealant to be visually checked, enables reliably filling of the periphery of a splice portion with the water sealant, and enables water in an unfilled region to easily drain. The wire harness waterproof structure includes electrical lines forming an intermediate splice portion, an exterior member surrounding the entire circumference of the intermediate splice portion and adjacent end portions, and a curing layer made up of a water sealant wherein a gap between the intermediate splice portion and the exterior member is filled. The waterproof sheet material is curved so as to surround the splice portion and the adjacent end portions. The sheet material has seeping holes allowing a portion of the curing layer to seep, and enable moisture to be drained to the outer surface in a region not filled with the water sealant.