An inertia locking-type waterproof connector is provided in which male and female connectors having a waterproof packing interposed therebetween are fitted together by an inertia force produced when abutting a retaining projection of an elastic lock arm against an engagement portion for engaging the retaining projection. The inertia locking-type waterproof connector includes a female connector housing, a male connector housing for connection with the female connector housing, and an elastic lock arm provided on one of the male connector housing and the female connector housing and having a retaining projection. An engagement portion is provided on the other of the male connector housing and the female connector housing. The engagement portion engages with the retaining projection. A packing is interposed between the male connector housing and the female connector housing for providing a waterproof seal. The packing includes a seal lip in sliding contact with either the male connector housing or the female connector housing. The retaining projection, engagement portion, and packing are positioned so that, during insertion of the male connector housing into the female connector housing, the initial abutment of the retaining projection with the engagement portion coincides with the initial abutment of the seal lip with either the male connector housing or the female connector housing.