A novel inbred maize variety designated PH8ER and seed, plants and plant parts thereof. Methods for producing a maize plant that comprise crossing inbred maize variety PH8ER with another maize plant. Methods for producing a maize plant containing in its genetic material one or more traits introgressed into PH8ER through backcross conversion and/or transformation, and to the maize seed, plant and plant part produced thereby. Hybrid maize seed, plant or plant part produced by crossing the inbred variety PH8ER or a trait conversion of PH8ER with another maize variety. Inbred maize varieties derived from inbred maize variety PH8ER, methods for producing other inbred maize varieties derived from inbred maize variety PH8ER and the inbred maize varieties and their parts derived by the use of those methods.