The results of study indicate that the starch content in tubers of potato cultivar was highly dependent on meteorological conditions during cultivation, storage time and less on potassium fertilization. Potassium used in a dose higher than 99 kg K∙ha-1 resulted in a decreased starch content. During storage period as a result of transpiration followed the increase of this polysaccharide content, however yield of the starch decreased. The content of reducing sugars after harvest was 0.31% and was on average about 30% lower than the total sugars content. Under the potassium fertilization reducing sugars content gradually decline, which positively affected the usefulness of the tested variety for processing. During storage, the content of reducing sugars and total sugars increased respectively by 52% and 30% in relation to content observed after harvest. The results indicate that the high potassium fertilization could be a factor limiting the accumulation of harmful sugars (especially reducing) in the process by storing potato tubers.