The validity of the weak equivalence principle (WEP) for massive bodies has been empirically confirmed with extremely high precision. However, can this principle be applied beyond massive bodies? The WEP states that every massive body falls at the same rate in a gravitational field. Does a massless body fall at the same rate within the same field? Theoretically, a body can be massive, negative massive, or massless. We aim to extend the WEP beyond massive bodies. To accomplish this goal, for negative massive bodies, we experimentally derive that the WEP applies to them in the same way as massive bodies do. For massless bodies, we conclude that only a type of massless body—with zero net mass—has a role in the WEP. On the basis of this condition, we conclude that the WEP applies to massless bodies. Therefore, we extend the WEP to massless bodies and negative massive bodies satisfactorily.