noun
biological parents
Refers to one's birth parents, as opposed to adoptive or foster parents. Used in formal and everyday contexts.
彼は実両親の顔を知らない。
He doesn't know the faces of his biological parents.
実の親 is a more common, slightly less formal way to say 'biological parent(s)'.
Compound of 実 (じつ, 'real, true') and 両親 (りょうしん, 'parents').