Background Overgrazing was assumed to increase the population density of small mammals that are the intermediatehosts of Echinococcus multilocularis,the pathogen of alveolar echinococcosis in the Qinghai Tibet Plateau.This researchtested the hypothesis that overgrazing might promote Echinococcus multilocularis transmission through increasingpopulations of small mammal,intermediate hosts in Tibetan pastoral communities.Methods Grazing practices,small mammal indices and dog Echinococcus multilocularis infection data were collectedto analyze the relation between overgrazing and Echinococcus multilocularis transmission using nonparametric tests andmultiple stepwise logistic regression.Results In the investigated area,raising livestock was a key industry.The communal pastures existed and the availableforage was deficient for grazing.Open(common)pastures were overgrazed and had higher burrow density of smallmammals compared with neighboring fenced(private)pastures;this high overgrazing pressure on the open pasturesmeasured by neighboring fenced area led to higher burrow density of small mammals in open pastures.The medianburrow density of small mammals in open pastures was independently associated with nearby canine Echinococcusmultilocularis infection(P=0.003,OR=1.048).Conclusion Overgrazing may promote the transmission of Echinococcus multilocularis through increasing thepopulation density of small mammals. Background Overgrazing was assumed to increase the population density of small mammals that are the intermediatehosts of Echinococcus multilocularis, the pathogen of alveolar echinococcosis in the Qinghai Tibet Plateau. This research works in the hypothesis that overgrazing might promote Echinococcus multilocularis transmission through increasingpopulations of small mammal, intermediate hosts in Tibetan pastoral communities. Methods Grazing practices, small mammal indices and dog Echinococcus multilocularis infection data were collected to analyze the relation between overgrazing and Echinococcus multilocularis transmission using nonparametric tests and multiple stepwise logistic regression. Results in the investigated area, raising livestock was a key industry. The communal pastures existed and the availableforage was deficient for grazing. Open (common) pastures were overgrazed and had higher burrow density of smallmammals compared with neighboring fenced (private) pastures; this high overgrazing press ure on the open pasturesmeasured by neighboring fenced area led to higher burrow density of small mammals in open pastures. medianbrorow density of small mammals in open pastures were independently associated with nearby canine Echinococcus multilocularis infection (P = 0.003, OR = 1.048) .Conclusion Overgrazing may promote the transmission of Echinococcus multilocularis through increasing thepopulation density of small mammals.