Thermal treatment is used for remediation of soils contaminated with both organic and inorganic contaminants. The target is destruction of organic contaminants while the residue containing the inorganic contaminants has to be further treated. The effects of thermal treatment on As, Cr and Cu in contaminated soil are evaluated in laboratory and field tests, using leaching test, As speciation and sequential extraction test. In laboratory tests on four particle size fractions, the leaching of As and Cr increased by factors of 18-40 and 2-23, respectively, while the mobility of Cu decreased 12-4 fold after thermal treatment. The concentration of As(V) in the finest soil fraction increased 19 fold, while As(III) remained constant. Arsenic, Cr and Cu associated to the reducible soil fraction decreased, possibly due to enhanced crystallisation of Fe oxides and reduction of available adsorption sites. In the field test, the concentration of As, Cr and Cu was 1-4 times higher in the filter fraction compared to the treated soil.