The purposes of the study arc to explore difficulties that native English speaking teachers (NESTs) experienced while co-teaching and to investigate their suggestions for better co-teaching. This study collected data from nine NESTs working at secondary schools in Korea through interviews. Regarding difficulties, the NESTs pointed out the hardships in relation to a lack of clear guidelines of co-teaching or role expectations, less active participation in class by Korean English teachers (KETs), and working with too many KETs for co-teaching. The NESTs made several suggestions for future co-teaching, such as provision of clearer guidelines to follow, decrease in the number of KETs to co-teach with, practical help in the format of co-teaching training and class observations, more interaction with KETs, and a new curriculum for co-teaching. Based on the findings, this study offers practical suggestions for better co-teaching.