To determinate self-purification constants of pollutants loaded in the ecosystems, the self- purification process was formulated, and a measurement method of the self-purification constants was derived. $C=C_0e^{-st}$ When $C_0$ is the initial pollutant amounts loaded in a ecosystem, and C is the rest pollutant amounts after the time, t, the equation of the self-purification, s, is $s=frac{P}{C}$ When in aquatic ecosystem, $C_0$ is the initial polluant amounts loaded in water body, and Cis the rest pollutation amounts after the time, t, the self-purification constant, s, is $s=(frac{ln C_0-ln C}{t}$ Self-purification constants of pine and oak forests at kwangneung in kyonggido were 0.07 and 10 respectively, of BOD in gokneung stream in kyonggido was 0.51, and of glucose and phosphate in pools on the stone in mt.jiri were 0.49 and 15.19 respectively.