Abstract: To evaluate the resistance in seedlings of 20 sugarbeet lines against two isolates of P. ultimum var. ultimum under greenhouse conditions, seeds were sown in sterilized soil treated with certain amounts of P. ultimum inoculum. Seeds of the line Rhizofort had already been treated with a fungicidal substance containing iprodion and hymexazol. The resulting seedlings were evaluated 3 week after sowing date. A zero to five rating system was applied to assess different levels of resistance. As a result of this evaluation, 16 lines were grouped as very susceptible and susceptible. The remaining 4 lines including 9597-P.58, 8150-Bulk, Mst231 and MstC2 appeared to be resistant to the infection. Also the line Rhizofort was grouped as the resistant because of its healthy appearance which might be due to the fungicidal treatment of the seeds. Results from this experiment revealed that the efficacy of resistance in the lines against damping-off, was more than the fungicidal treatment of the seeds.