Background and aims: Inoculation with Penicillium bilaii has been reported to increase plant growth, which is attributed to increase availability of phosphorus (P), but similar effects have been observed with no P limitation, suggesting that other mechanisms may be involved. The aim of this work was to evaluate the interaction between available soil P and P. bilaii inoculation on plant growth. Methods: Maize plants (Zea mays) inoculated with P. bilaii and non-inoculated were grown in pot experiments in three soils with different inherent P availability, and in a low P availability soil with different additions of mineral P, both with and without supplementation of all other macro and micronutrients. Results: We found a positive interaction between P bilaii and available P, when other nutrients were applied, with P bilaii inoculation resulting in increased root growth and thus nutrient uptake and plant growth. By contrast, when other nutrients were not supplied, little effect on plant growth or P uptake was observed, except for root length that tended to decrease in inoculated plants with P addition. Conclusions: The effects of P. bilaii inoculation were related to root growth and function, but were dependent on the nutrient status in the soil environment.