Youn-gug Yang. 2001. Some Theoretical Effects and Problems is Agree Operation. Studies In Modern English Grammar 23, 95-106. This paper attempts to review theoretical effects of a new version of feature checking theory of Chomsky (2000), and to discuss its problems in terms of matching relation between a probe and a goal. To maximize the theoretical effects of Agree operation, this paper, focusing on Case, presents the following assumptions; a. Case features should be differentiated as nominative, null and accusatives. b. Functional categories, T and u bears Case as an inherent properties respectively in the lexicon: T bears nominative Case and u, accusative. c. Case should be deleted under matching between a probe(=the Case feature of T/u) and its goal(=that of a substantive category).