A two year-experiment was carried out to study an effect of root inoculation with arbuscular mycorrhizal (AM) fungus on soil mineral concentrations and soil microbial activity in grapevine (Vitis vinifera) cv. "Cabernet Sauvignon" cultivated in Chile. Plants were inoculated with a commercial granular inoculant (Mycosym Tri-ton®) and cultivated in 20 L plastic pots filled with an unsterilized sandy clay soil from the Vertisols class under climatic conditions of Curicó (34°58' S; 71°14' W; 228 m ASL), Chile. Soil analyses were carried out at the beginning of the study and after two years (four samples of rhizospheric soil for each treatment) to assess the effects of mycorrhizal infection on soil mineral concentration and physical properties. Soil microbial activity was measured by quantifying the soil production of CO2 in ten replications of 50 g of soil from each treatment. Root mycorrhizal infection was assessed through samples of fresh roots collected during 2005 and 2006. Fifty samples for each treatment were analyzed and the percentage of root length containing arbuscules and vesicles was assessed. During both years (2005 and 2006) all treatments showed mycorrhizal infection, even the Control treatment where no AM was applied. Mycorrhizal colonization did not affect the soil concentrations of N, P, K, Ca, Mg, K, Ca, Mg, Mn, Zn, Cu, Fe, B, organic matter, pH/KCl and ECe. Soil CO 2-C in vitro production markedly decreased during the period of the study. No significant differences where detected among treatments in most cases.