Several studies have concluded that mountainous countries such as Nepal are more vulnerable to climate change; thus, a changing climate should have a significant impact on crop yields. This work aims to explore the impact of climate change on major crop yields in the mountainous parts of Nepal and to determine their relationships based on a regression model between historical climatic data and yield data for food crops. The study starts with an analysis of the last 30 years of climatic data from Lamjung district. Mann-Kendall and Sen’s Slope methods have been used for the trend analysis and quantification. The results showed an increase in temperature of approximately 0.02 °C to 0.07 °C per year in different seasons and a mixed trend in precipitation. Although there was no significant impact of the climate variables on the yields of all crops, the regression analysis revealed negative relationships between maize yield and summer precipitation and between wheat yield and winter minimum temperature, and a positive relationship between millet yield and summer maximum temperature.