The decay of virioplankton is one of the most important process of virioplankton population dynamics. Besides the solar-ultraviolet radiation b, other factors can also lead to the decay of virioplankton. Experiment was carried out to study the decay rate of cyanophage PP caused by some environmental factors: non-UVB radiation in sunlight, particle materials, heat-sensitive substances and water temperature. The results indicated that the decay rate of cyanophage PP by the non-UVB radiation part of sunlight at noon was 3.8%.h(-1), however, the decay rate was swiftly attenuated to less than 1.0%-...