This study was intended to investigate the characteristics of loads acting on the transmission of agricultural tractors during plowing, rotavating and transporting operations. A survey was conducted to determine working speeds and transmission gears most frequently used for each operations. The transmission loads were measured at the input shaft of the transmission gear box during each operations. Time histories of the measured torque loads were converted into a load spectrum and analyzed with respect to the S-N curve of the shaft material to estimate the partial damages on the transmission. Finally, comparison of the relative damages and severeness of each operation was presented and discussed.