The present invention provides a method for determining the efficacy of a GPC3-targeting therapeutic agent for a liver cancer patient and a GPC3-targeting therapeutic agent or a preparation which is to be administered to a patient for whom it has been determined that the GPC3-targeting therapeutic agent is effective. The present invention provides, for example, a method for determining that a GPC3-targeting therapeutic agent is effective when the expression level of GPC3 per tumor cell is a predetermined value, and a GPC3-targeting therapeutic agent or a preparation which is to be administered to a patient for whom it has been determined that the GPC3-targeting therapeutic agent is effective.
