Abstract: Objective To study the possible seasonal difference of the diatom detected in the organs of the drowned for helping determine the death cause in forensic investigation. Method 5 cases per month drowned in Hun river in January, April, July and October from 2009 to 2011 were collected. 45 rabbits were used for experiment and divided into three groups, i.e. drowned, immerging into water after death and the control. Rabbits were put into water at the same spot on the next day of body discovery in the corresponding month. Lung, liver, kidney and femoral bone marrow samples of bodies and rabbits, as well as the on-site water samples, were tested for diatom by enzymic digestion method. Results Abundant diatoms were detected in the lung of dronw. ned bodies and they were the same species as those detected in the on-site water samples. A small amount of minor centricae diatoms were found in the liver and kidney of bodies drowned in January, April and October, but none in the liver, kidney and marrow of bodies drowned in July. In the case of rabbits, a small amount of minor centricae diatoms were found in the lung of drowned rabbits, but no diatoms were found in the liver, kidney and marrow. Conclusion The seasonal difference in diatoms detected in the liver and kidney might be related to the seasonal change of diatom species and their volumes. With positive results of diatoms in lung and negative results in liver and kidney, drowning cannot be ruled out as the cause of death.