This study investigates professors' and students' opinions on English-medium instruction (EMI) at three major engineering universities in Korea in an attempt to offer sound suggestions for the improvement of EMI. The three engineering universities that have most actively implemented EMI among Korean universities during the last decade were chosen for this survey study. Questionnaire surveys were conducted among the undergraduate students and instructors teaching undergraduate courses at the universities in the spring of 2014. Survey results show that the majorities of both groups chose EMI courses due to their school policies (rather than for academic or instructional considerations or benefits), thought that students had inadequate English skills for EMI, were more satisfied by Korean-medium instruction (KMI) than by EMI, but still believed that their schools should continue with EMI. Moreover, the two groups differed in their opinions on effective methods of EMI. The study reviews studies on EMI methods (Doiz, Lasagabaster, & Sierra, 2012; Fortanet-Gomez & Raisanen, 2008; Wilkinson & Walsh, 2015) and concludes with suggestions for the improvement of EMI in the context of Korean engineering universities.