The present study investigated the underlying cognitive mechanism of the truth-value validation process of Korean comparative structure sentences. The brain and behavioral response of 15 Korean native speakers were recorded and analyzed during the processing of the comparative sentences with 4 conditions manipulated by the frequency of the predicate (big or small) and the truth-value(true or false). The behavioral results (i.e. judgment time and accuracy) showed that only the effect of the predicate’s frequency was significant. However, in the ERP, the predicate’s frequency effect and the truth-value effect were reflected in early N400 component(250-400ms) as well as the positivity effect in 400-600ms by the truth-value factor. The immediacy of the truth-value validation and the functional interpretation of N400 related to the truth-value were discussed in overall.