Palabras clave: bioinoculantes, calidad, diazotrofos, fijacion biologica de nitrogeno ABStRAct: Alnus acuminata H. B. K. is a tree species which can be incorporated in silvopastoral systems, because it has the capacity to grow on marginal soils and contribute to the conservation of biodiversity and to soil amelioration; which is related to the incorporation of litter, effect of shade, retention of humidity, nutrient recycling and fixation of atmospheric nitrogen, due to its symbiotic association with the actinomycete Frankia. The use of Frankia as inoculant is a technology that requires a deep analysis of its performance under controlled conditions. On the other hand, for the commercialization of biofertilizers it is important to preserve their quality as long as possible, on which the acceptance of the product in the productive chain depends. For such reason, a study was conducted in order to evaluate the biological stability of the native Frankia strains (Aan17 and Aac49) with different substratum:strain proportions, as well as the effect of storage at 4 oC. The strains were tolerant to the pH changes and the storage under refrigeration conditions. It is concluded that the inoculants should be stored at 4 oC during 120 days, with a proportion of 80:20 (inoculant:substratum) in Aan17 and 60:40 in Aac49. In these substrata the microbial protein remained over 0,65 mg/mL in Aan17 and 0,7 mg/mL in Aac49.