In 2006 rose cultivation in the municipalities of Tenancingo, Villa Guerrero and Coatepec Harinas covered an area of 415 ha, representing a significant production value equivalent to 688,722,450.00 pesos. This crop is attacked by white root rot disease, resulting in plant losses since control methods are ineffective. The objectives of this study were to identify the fungus species associated with white root rot disease in rose plants and evaluate its sensitivity to fungicides. Samples of plants with infected roots were collected in Tenancingo, Villa Guerrero and Coatepec Harinas in the State of Mexico, obtaining nine strains. The fungicides quintozene, benomyl, fluazinam and thiophanate methyl were evaluated at doses of 1 g.L1, 0.6 g.L-1, 0.5 ml.L-1 and 0.6 g.L-1, respectively. The fungus associated with white root rot disease presented mycelium with pyriform swellings before the septum; as symptoms, mycelial cords were found on the root and neck of the plant. The fungus was identified taxonomically as Rosellinia necatrix Prill. (Dematophora necatrix (Hart.) Berl.), which was confirmed by mole¬cular analysis. The strains T1GRJ, T2GRJ and T3GRJ of Tenancingo and the strains VG1GRJ, VG2GRJ, VG3GRJ and VG4GRJ of Villa Guerrero were insensitive to the fungicide quintozene, while with the fungicides benomyl, thiophanate methyl and fluazinam no mycelial growth appeared. The strain T4GRJ of Tenancingo showed sensitivity to all fungicides. The strain CH1GRJ of Coatepec Harinas was insensitive to quintozene and presented slight growth with fluazinam, while with benomyl and thiophanate methyl there was no growth.