In 2016, South Korea experienced extremely high temperatures and the Korea Centre for Disease Control and Prevention (KCDC) reported 17 heat-caused deaths during these heat waves, most due to heat stroke. Because the reported number of heat-caused deaths is only part of the total deaths associated with heat waves, we aimed to estimate attributable deaths during heat wave episodes. We linked mortality to meteorological data in 16 regions in South Korea and estimated relative risk at or above threshold of maximum temperature during summer using generalized linear regression models after controlling for confounders. We computed overall, age-, sex-, and cause-specific attributable deaths from 2006 to 2017. With a 1.5% increase in all-cause mortality per 1 °C increase in concurrent days' maximum temperature during summer, this study estimates a total of 1440 all-cause deaths associated with heat waves during the 2006-2017 study period in South Korea. We estimate that 343 deaths in 2016 can be ascribed to heat waves, which is approximately 20 times more than the number reported by the KCDC (17 heat-caused deaths). This study addresses attributable heat wave deaths in South Korea and illustrates that the reports of medically classified heat-caused deaths seriously underestimate the number of deaths attributable to heat waves. Our findings may enable the implementation and reinforcement of government- and individual-level management strategies for heat waves.