Batch digestion experiments of biological sludge by continuous aeration and intermittent aeration were performed to find the release characteristics of nitrogen and phosphorus in this study. Nitrogen content of the sludge increases for the endogenous respiration period, but the content gradually decreases to the same content of raw sludge. Nitrogen removal efficiency was up to 42.7% for 34 days by the intermittent aerobic digestion of which aeration ratio was 0.25 and the removal efficiency was dependent on aeration ratio. Phosphorus does not release until the phosphorus content reaches a limit content. So, phosphorus content of sludge increases gradually to this limit. After the phosphorus content of the sludge reaches this limit, phosphorus will be released proportional to VSS reduction rate.