Diarrhea is reported as one of the most common diseases in calves. It is thought to be a major cause of productivity and economic loss to cattle producers. The aim of this study is to provide a better under-standing of well-known diarrheagenic pathogens and incidence of diarrhea in Korean calves. In this study, the relationship of calf diarrhea and pathogens were investigated from calves under 60 days of age in five areas of Korea from April to July, 2016. Of examined fecal samples, 38.3% was positive for any pathogens, and Giardia was the most common pathogen (25.5%). The incidence of diarrhea was 31% from pathogen-negative fecal samples whereas 61.1% from pathogen-positive fecal samples, sug-gesting high correlation between pathogenic factor and diarrhea. In addition, 80% of E. coli (K99) pos-itive calves showed diarrhea, suggesting E. coli (K99) could be highly pathogenic. The incidence of diarrhea and infection rate increased with age. Rotavirus was revealed as a major pathogen in calves under 20 days of age, and the infection rate of Giardia increased rapidly in calves 20 to 39 days of age. The information on interconnections between clinical diarrhea and pathogens would contribute to developing strategies for treatment of calf diarrhea.