Effects of nitrification on BOD were evaluated with two kinds of batch experiments, and the problems caused by N-BOD were discussed with descriptions of test manuals, experimental data and literature review. The main results drawn in this study are as follows:(1) most of water analysis manuals do not clearly describe nitrification on BOD test is an interference nor the matter to be measured, (2) ammonium nitrogen in dilution water causes a positive error in BOD test, and can overestimate N-BOD values more than two times, (3) BOD values measured with present methods can not express the pollution level because of N-BOD appearance during the purification development. As a conclusion, it is recommended that oxygen consumption by nitrification should be eliminated from the contents of BOD, and the test procedure should adapt an inhibition process for nitrification in BOD measurement.