Korean is a language that have both postpositional particles of topic marker (-eun/ neun) and nominative marker (-i/ga). The purpose of this study was to examine the acquisition of these particles in view of agentivity. We defined agentivity of a particle as the probability in which a noun phrase with the particle is processed as the agent of a sentence. Eighty Korean native speakers of 4, 5, 6, 8, 10, 12, 14 years old and adults were instructed to listen to simple noun-noun-verb sentences and to judge which noun was the agent by acting out the sentences using miniature animals and objects. Stimulus sentences consisted of 18 sentence types composed of particle (3) × word order (2) × noun animacy (3) combinations. The results showed that the agentivity of the nominative maker was higher than that of the topic marker in the adult's responses and it was at twelve years old when the level of agentivity came up to an adult's level. This tendency was quite similar to the way of the processing of Japanese particles: topic “-wa” and nominative “-ga”.