Since the horizontal global radiation and cloud cover are a main factor for designing any solar photovoltaic system, it is necessary to evaluate its characteristics all over the country. The work presented here are the investigation of horizontal global radiation and cloud cover in Korea. The data utilized in the investigation consist of horizontal global radiation and cloud cover collected for 27 years(1982. 12~2008. 12) at measuring stations across the country. The analysis shows that the annual-average daily horizontal global radiation is $3.61;kWh/m^2$ and the annual-average daily cloud cover is 5.1 in Korea. We also constructed the contour map of cloud cover in Korea by interpolating actually measured data across the country.