This article presents the results of a study of the parameters of acute toxicity and sensitizing properties of a microbiological additive based on probiotic strains L. acidophilus IV138 and B. subtilis GA24 on White Wistar rats and White Giant rabbits. The acute toxicity class of the prototype feed additive was established in accordance with the fundamental document OECD Test № 423 “Acute Oral Toxicity - Acute Toxic Class Method” (2001). The evaluation of the irritating properties of the microbiological preparation was carried out by the method of skin applications and using the test conjunctival test. The research results showed that the probiotic preparation does not have acute toxicity when administered orally to warm-blooded animals, sensitizing properties in the conjunctival test and skin application. According to the results of experimental studies, the feed additive containing L. acidophilus IV138 and B. subtilis GA24 strains is classified as a low-hazard product.