The common vole permanently inhabits Bulgarian agricultural ecosystems, forming colonies. It is the most numerous pest species among small murine rodents. The considerably increased damage caused by harvest murine rodents and especially by the common vole in Bulgaria in years is undoubtedly also promoted by climatic changes in the whole country during drought. The analysis of population dynamics should cover a region which is homogenous in regard both to climatic conditions and to structure and composition of the main agricultural ecosystems, inhabited by the vole. The dynamics of the common vole population under specific climatic conditions in agricultural ecosystems in northeastern Bulgaria was based on development of the vole population throughout a period of 30 years in alfalfa and winter wheat fields, localized in the Dobrich region. The development of a new region of strong pest infestation in northwestern Bulgaria has been confirmed.