The current study compared the use of conjunctive expressions to indicate disagreement by native and non-native speakers of Japanese during a problem-solving task. Three levels of English-speaking learners of Japanese were asked to work in pairs to find a solution to a given problem. A group of native speakers were asked to perform the same task. The conversation during the task was audio-recorded and transcribed for analysis. The results revealed that the learners often used conjunctive expressions in expressing a lack of agreement, while native speakers used very few. High-intermediate learners predominantly used the adversative conjunction demo, while advanced learners used other conjunctive expressions, such as kedo and kara, in addition to demo. In the consensus-building phase, native speakers often delayed their responses to prompt their interlocutors to adjust their opinion. In contrast, advanced learners used demo for the same purpose, while high- and low-intermediate learners used demo and kara excessively.