This study investigates English L1 and L2 talkers` mutual intelligibility of focus speech. Speech intelligibility of non-native talkers by native listeners has been much examined in L2 studies, but L1 talkers` intelligibility for L2 listeners is relatively less highlighted although the success of speech communication between natives and non-natives depends on mutual comprehension. Therefore, both native and non-native talkers` mutual intelligibility is investigated in the identification tasks of focal prominence, Two perception experiments were conducted to measure Korean talkers` intelligibility of focus intonation for native listeners and similarly native talkers` intelligibility of the same stimuli for Korean listeners. Non-native Korean talkers and listeners` proficiency and focus type were varied. Listeners` accuracy and reaction time were measured, and all the data were statistically analyzed. Results showed that native listeners were more accurate at identifying broad and narrow focus sentences than contrastive focus ones, but that their reaction time was significantly more prompt to narrow focus stimuli than broad and contrastive focus stimuli. This suggests that Korean talkers are the most intelligible for narrow focus, next broad focus and the least intelligible for contrastive focus. Native talkers` intelligibility, on the other hand, did not seem to be affected by Korean listeners` proficiency or focus type. Both non-native Korean and native talkers were highly to moderately intelligible unlike segment intelligibility. This might be attributed to the fact that the listeners took advantage of top-down processing, utilizing contextual cues available in a whole sentence.