Abstract: Trichoderma harzianum and T. viride were evaluated for their antagonistic activity against F. oxysporum f.sp. tuberosi, F. solani, F. graminearum and F. sambucinum causing potato dry rot in Tunisia. In vitro dual culture experiments, observed after incubation at 25°C for 6 days, showed that both tested Trichoderma species significantly reduced mycelial growth of Fusarium spp. comparatively to untreated controls and that a significant interaction was noted between both fixed factors (at p≤0.05). Light microscopic studies of antagonists x Fusarium spp. in vitro interactions showed lesser mycelium density, severe lysis, lesser pathogen sporulation, mycelial cords formation and early chlamydospores induction which were observed only at the confrontation zone of both microorganisms. Potato tubers, cv. Spunta, individually treated, at inoculation sites by 100 μL of Trichoderma spp. suspensions (108 spores mL-1), 24 h prior inoculation by Fusarium species, showed reduction in dry rot development, after 21 days of incubation at 25-27°C, comparatively to untreated controls.