A laboratory and pot experiment was conducted to assess the effectiveness of Phosphate Rock (PR) and biosolids (composts) as chemical amendments for the in situ remediation of heavy metals-contaminated soils. Chemical treatments included raw, acidulated PR at 25% (PR-25), and at 50% (PR-50), and composted biosolids (sugarcane by-products), which were applied in single and combined doses to three calciorthids soils. The effects of soil treatment on metal extractability were measured by a sequential extraction and on metal phytoavailability to maize (Zea mays L.) through a pot experiment. The distribution of metals within the extraction fractions varied among metal species, chemical treatments, and soil properties. Concentrations of water soluble metal fractions were low in most soils, and metal concentrations from the second extraction followed a similar pattern because percent of exchangeable metal was not in general higher than 10% across soil treatments. In contrast, most soil treatments showed significant difference for the remaining non-residual fractions. Variation in the effect of soil treatment on metal immobilization was reflected through the calculated E-values of metals extracted from the first extract of the sequential procedure. The application of PR-50 combined with composts in S2 soil decreased the concentration of Ni (30%), Cd (37%), and Pb (53%), in maize leaf. Effect of this treatment was more pronounced in S3 soil where Ni concentration in maize leaf showed the largest reduction 46% and that of plant Pb amounted to 70%, suggesting that for most of the metals, a soil barrier limit for metal transmission to the plant may be resulted from the application of these chemical amendments to the soils through metal immobilization process.