Which issues do political parties emphasize in campaigns? Selecting the issues to emphasize in campaigns is treated with the same importance as policy positioning. Nevertheless, little attention has been paid to understanding parties' strategies of issue competition in presidential elections under multiparty systems. By analyzing statements of presidential candidates in the 2002, 2007, and 2012 Korean presidential debates, we find that presidential candidates use their issue emphasis strategies differently in presidential elections according to party size and ideological relationships with other parties. Specifically, a small party's candidates have been more likely than mainstream parties' candidates to pursue their issue ownership advantage. In addition, a mainstream party's candidates have emphasized the issues of a small party more than those of his own party when the two parties have had a similar ideological foundation, whereas, when there were no such ideological similarities, a mainstream party's candidate has only focused on issues of the mainstream party. Our results imply that the political communication used by political parties and candidates is conditioned not only by political contexts such as electoral systems or party systems but also by the size and ideology of parties.