Compost addition to soil improves soil fertility, valorizes organic wastes and is expected to decrease the mobility of toxic metals by sequestration into soil organic matter. On the contrary, we hypothesized here that compost addition may increase metal mobility in metal-rich soils. For that, we studied the mobility of copper, zinc, nickel and chromium in Ferralsols by kinetic extraction with ethylenediaminetetraacetic acid. Results show an increase in the extractable metal pools in the compost-amended Ferralsols, amounting up to 500 mg of nickel per kg and 100 mg of chromium per kg, representing 10% and 1% of the total concentrations. The enhanced mobility of nickel and chromium arise most probably from soil properties, while the enhanced mobility of copper and zinc should mainly originate from compost properties. We conclude that addition of compost may induce the release of toxic metals in substantial amounts under specific conditions.