Several leaching tests were conducted for sewage sludge and their re-products to investigate the characteristics of heavy metal release. Regarding incinerated ash, leaching tests indicated that the concentrations of Se and As in leachate were relatively higher than those of other heavy metals. The ratio of As extracted into leachate varied according to the leaching test method. The lower the pH value of leachate after the leaching test, the higher the concentration of As observed. The data using the Holland method had the highest value, and 19.7 – 46.9% of As was extracted into leachate. If the ratio of concentration in leachate to content (L/C) by the Holland method is 1.00, that of other methods was 0.20 – 0.43. Regarding melted slag, leaching tests indicated that the heavy metal concentrations in leachate were very low. Regarding re-products, leaching tests indicated that the heavy metal concentrations in leachate were much lower than those of incinerated ash and melted slag. The diameter effect of crushed sample was investigated by the Holland method. 0.3 – 0.7% of As was extracted from the crushed samples having diameter 20 – 50 mm and 0.9 – 2.6% of As was extracted from the samples having diameter less than 5 mm.