Two field experiments were conducted at Ali Mubarak Horticultural Experiment Station, Behera Governorate, Egypt in split plot design during two successive seasons 2014/2015 and 2015/2016 to evaluate the effect of two types of bentonite (black and brown) and varied levels of K- fertilizer i.e., 0, 50, 75 and 100% of the recommended dose (100 kg fad.^-1), on some vegetative and yield parameters of potato plants and also their effect on some sandy soil properties. The results indicated significant increase for bentonite types on each of EC, CEC, OM, WHC, FC and available NPK of sandy soil. Meanwhile, their effect on soil pH was non significant. The difference between the influences of the two types of bentonite were non significant for all studied parameters of the soil except CEC, WHC and FC where the difference was significant. The effect of K-levels on the forenamed properties was non significant except available K. The interaction effect was non significant  for all soil parameters except available N and K. Application of 15 ton/fad., from either black or brown bentonite or K-fertilizer levels solely as compared with the control, increased significantly the growth and yield parameters of potato plants. The black bentonite was superior to the brown bentonite on yield parameters. The highest effect was obtained when the soil treated with bentonite and K-fertilizer together. Foliage content of NPK affected significantly by applying 15 ton/fad., of bentonite but the differences in the influence between the two types were non significant. The tuber content of NPK, starch and protein affected significantly with the two types of bentonite but the black was better than the brown in this concern. Increasing K-fertilizer increased significantly foliage and tuber content of NPK while the interaction effect of bentonite + K- fertilizer was better than each alone.