The microfungus Beauveria bassiana is known as an insecticidal agent, but recent studies imply that it forms a mycorrhiza-like interaction with the plant host. Previous studies confirm the mentioned interaction in strawberry, bean, tomato, cabbage, cucumber, barley, wheat and corn crops, vines, but studies in lettuce cultivation is scarce. The goal of the research is to test the "mycorrhiza-like interaction" of the autochthonous isolate B. bassiana on the growth and development of lettuce (Lactucae sativa, variety Australiae RZ) in greenhouse conditions. Repeated application of B. bassiana conidia suspension was carried out in the phenophase of 2-3 lettuce leaves (BBCH 12-13), by watering the plants in the root zone for five weeks. In order to quantify the potential of B. bassiana to promote lettuce growth through a potential mycorrhizal interaction, the weight and rosette and roots area of each plant were weighed. The results confirm a significant increase in the root area of the plants (by 31.6% and 30.5%) treated with the conidia suspension, compared to the control group, when the plants were treated every and every other week. Significantly higher biomass of plants (by 16.7% and 20%) was recorded in all test variants compared to the control. The rosette area of the treated plants did not differ significantly compared to those from the control group. By re-isolating the microfungus from the roots of plants treated every and every other week, the potential of B. bassiana to promote the growth of lettuce (as a result of mycorrhizal-like interaction) in greenhouse conditions was confirmed but also that it did not persist in the plants after 10 weeks. The obtained results are a confirmation of modern studies that shows similar results on various plant species. Also, B. bassiana shows the ability to interact like mycorrhizae fungi with lettuce roots, but additional research in in vivo conditions is needed to better understand this form of interaction.