Growing maize in calcareous soils requires adequate supply of phosphorus inputs, yet excessive P-applications may affect negatively micronutrients availability in soil, including Zn. Thus, the current study evaluates the ability of humic acid (HA) to counteract the negative effect of applied P on Zn-uptake by maize plants. To achieve this aim, a field experiment was conducted in a calcareous soil (CaCO3 =268.91 g kg-1) following a split plot design to study the interactions between different P-inputs (100, 125 and 150% of the recommended dose, applied in main plots) and available-Zn in presence and absence of HA (applied in sub-plots at either 2 or 4 kg HA ha-1). Results revealed that increasing the level of P-application raised significantly P availability and consequently its uptake by maize plants; thus, enhanced significantly plant growth parameters and grain yield. In this concern, 125% of the recommended P-dose recorded the highest partial-factor-productivity values. Likewise, application of HA raised significantly available-P content and improved considerably plant growth and grain yield, especially with increasing the rate of its application. On the other hand, increasing the level of P-fertilizers decreased significantly Zn-availability and uptake by plants; however, in presence of HA, this effect was counteracted. Although, this amendment recorded no significant effect on soil-Zn availability; however, it raised significantly its content in shoots but not in grains. In conclusion, HA improved significantly productivity of maize grown on a calcareous soil. This amendment not only improved the partial factor productivity of P-fertilizer, but also increased Zn-uptake by maize plants.