K is an essential nutrient because it is required for many metabolic processes and its role cannot be substituted by other nutrients (Westermann, 2005). In this research K2SO4 was used as source of K2O. The findings agree with Stark et al. (2004) and Kumar et al. (2007) that K can increase yield, the proportion of process-grade tubers, and tuber and chips quality. Bansal and Trehan (2011) reported that K fertilizer application increases tuber size but not numbers. It can increase yield by increasing numbers and yield of large sized tubers. Moreover, Singh et al. (2010) reported that application of 100 kg ha-1 K2O fertilizer increased numbers as well as yield of large (>75g) and medium-large (50-75g) tubers which increased overall tuber yield and marketable yield. Our research was conducted in different soil condition, potatoes variety, source of K fertilizer and levels of fertilizer application compared to previous work. Although the quantity of yield was similar, addition of K2SO4 fertilizer can increase numbers of process grade tubers. Therefore K2O can be proposed to obtain higher proportion of processed grade tubers.