Aim Potassium (K) is a key determinant for plant development and productivity. However, more than 90% of K in the soil exists in an insoluble form. K-solubilizing microbes play an important role in the transformation of insoluble K. Thus, the objective of this study was to evaluate K-dissolving ability of Aspergillus aculeatus (F) and growth-promoting properties in perennial ryegrass. Methods and Results Perennial ryegrass inoculated with A. aculeatus exhibited enhanced soluble K accompanied with higher growth rate and turf quality, compared with the non-inoculated regimen. In addition, A. aculeatus also played a primary role in increasing chlorophyll content and photosynthetic capacity of the plant exposed to LK + F (K-feldspar plus A. aculeatus) treatment, compared with CK (control, no K-feldspar and A. aculeatus), F (only A. aculeatus) and LK (only K-feldspar) groups. Furthermore, the antioxidase activities (CAT and POD) were significantly increased while the oxidative damage (EL and MDA) was dramatically decreased in LK + F group compared to the LK (K-feldspar) group. Finally, in perennial ryegrass leaves, the genes expression levels of HAK8, HAK12 and HKT18 were obviously elevated in LK + F group, compared to CK, F and LK groups. Conclusion We concluded that A. aculeatus could solubilize K from bound form and be considered as K-solubilizing biofertilizer through supplementing K in soil. Significance and Impact of the Study A. aculeatus has potential to be used as biofertilizer in sustainable agriculture.