Abstarct: Despite the importance of potassium (K) in biotic and abiotic stresses, this necessary element could be fixed easily in the soil which reduces its utilization efficiency. This study aimed to evaluate K solubilizing bacteria (KSB) along with different amounts of potassium sulfate fertilizer on rapeseed (Brassica napus L. cv. ‘Hayola 50’) in a saline and a non-saline soil. The experiments were performed in split plots baxsed on a randomized complete block design with three replications in 2018-2019. Treatments including potassium sulfate fertilizer (50%) in seven levels (control, 25, 50, 75, 100, 125 and 150 kg/ha) as the main plot and KSB isolates in five levels including control or uninoculated, Pantoea agglomerans (Pa), Rahnella aquatilis (Ra), Pa+Ra and a commercial K biofertilizer named Barvar 2 (Pseudomonas koreensis and P. vancouverensis) were used as subplots. Biological yield, grain yield and seed oil, uptake of sodium and potassium in the soil and plants were measured and potassium efficiency indices were also calculated. The results showed that grain yield, biological yield, oil yield and potassium uptake in seeds and stems increased by 8.6-40.1, 4.5-6.31, 8.7-12.62, 0.8-6.23 and 1.1-13.5% non-saline conditions and 6.3-4.0, 3.7-33.9, 4.2-9.71, 2.21-7.0 and 4.2-21.1% in saline soil increased as compared to the control treatment. In terms of KSB treatments, the maximum value for all the studied traits was recorded in Pa+Ra combination in both non-saline and saline soils. Regression analysis indicated that simultaneous inoculation of KSB not only reduced 10.9 and 13.9 kg/ha (13.3%) of K chemical fertilizer but also increased the grain yield by 1226.4 and 305 kg/ha (11.7 and 39.7%) as compared to the control in non-saline and saline soils, respectively. These results confirmed that KSB isolates can be used in sustainable rapeseed cultivation.