Abstract: A lightweight burial vault made entirely of plastic with appropriate stabilizers and additives which can be sealed so as to be moisture proof and has sufficient strength and durability to withstand the loading forces of the fill earth, comprises a base unit forming the floor of the vault and a dome-like cover having a concave top integrally molded to the upstanding side and end walls thereof. A system of ribs is formed integrally to the outside of the cover, and means are provided for sealing the cover to the base unit. The base unit may have a plurality of spaced apart troughs extending thereacross to collect fluids inside the vault.