The amount of incinerator ash of sewage sludge produced in wastewater treatment plants in Japan has increased year by year as the percent of sewered population increases. The incinerator ash is considered to be hopeful resource of phosphorus, because phosphate ore has some fear for the exhaustion in the world today. In this study, the influence of temperature on alkaline elution of incinerator ash of sewage sludge was investigated using X ray analysis and elution experiments. Heating alkaline elution of incinerator ash at 40°C eluted phosphorus without the elution of zinc. It was found that the substance eluted from incinerator ash was aluminum phosphate which occupies about 50% of total phosphorus compounds contained in the ash.