This research was carried out to investigate the role of non-farming activities in the sustainability of peasant farming systems in Osku County by a descriptive-correlational research method. The research population consisted of peasant farmers in Osku County (N =1400), out of whom 300 people were sampled based on Krejcie and Morgan’s table for sample size determination using the proportionate stratified sampling technique. Data were analyzed by SPSS win18 software. The main instrument of data collection was a questionnaire whose validity was confirmed by experts. The reliability of the main scales of the instrument was confirmed by Cronbach's alpha coefficient, which was in the range of 0.82-0.87. The results of analyzing three dimensions of sustainability showed that, in total, 29.3 percent of the farming units were "unsustainable", 41.7 percent were "semi-sustainable", and 28.9 percent were "sustainable". Based on the regression analysis, the variables of the number of people employed in the non-farming sector, the use of non-farming income in the agricultural sector, and household income out of non-farming activities accounted for 54.2 percent of the variations in sustainability level of the peasant farming systems. پرونده مقاله