Research shows increasing frequency of climatic variability and extreme events throughout Nepal. However, there are not specific studies on the Koshi basin, one of the most important basins of the country in term of livelihood and economy. This study explores the pattern of climate change over the Koshi basin based on observed data from 1970 to 2010. The basin covers a total area of about 60400 km2 . The Koshi River and its tributaries, through agriculture and other natural resources, support approximately 5.2 million people living in this basin. Any changes in climate will have significant impacts on the agricultural based communities of Koshi.