A field experiment was conducted at EL- Kassassien Agric. Res. Station (ARC), EL- Ismaielia Governorate in the winter season of 2007 / 2008, to study the effect of inoculation with either Bacillus circulans (Silicate (potassium) dissolving bacteria or cyanobacteria (nitrogen fixers and plant growth promoters) on the availability of potassium from both potassium sulfate (48 % K₂O) and feldspar (10.5% K₂O) as a natural source of potassium to potato plants, as wall as, to investigate their effect on potato yield and its characters and soil available N, P and K contents after potato harvesting and soil biological activities. Results indicated that inoculation with B. circulans and/or cyanobacteria (biofertilizers) in the presence of different potassium sources increased all examined potato tuber yield, tuber content of carbohydrate and soluble sugar, soil biological activity and soil available N, P and K compared to the sole use of K- sources. The dual inoculation with bacteria and cyanobacteria in combination with both K-sources at both tested levels surpassed all the tested treatments and gave the highest potato tuber yield with priority of K- sulfate source than K- feldspar source. However, the use of potassium (K-rock) minerals in combination with biofertilizers may be agronomically more useful and environmentally more feasible than soluble K.