Abstract: This paper has analyzed self-citation rate of 548 Chinese college journals natural science published during 2005-2007,and fixed normal reference range for self-citation rate of each year.The reference range thus provides reference for the defining of over self-citation thereof.Study shows that self-citation rates of Chinese college journals of natural science during 2005-2007 are as follows respectively:0.100±0.096，0.086±0.090 and 0.078±0.077,declining year by year.The maximum of self-citation rates during 2005-2007 are as follows:0.257，0.234 and 0.204.From 2005 to 2007,over self-citation existed in 39(7.12%),35(6.39%),and 37(6.75%) of Chinese college journals of natural science.

Key words: journal, self-citation, impact factor