Soil avocado with symptoms of chlorosis and defoliation that were associated with Phytophthora cinnamomi in the orchards of two valleys (Azapa and Codpa) in northern Chile were explored, in this soil the EC and pH was measured in the saturation extract. The phytopathogen was successfully isolated using as bait circles of leaves of Eucalyptus globulus, was identified in only one of the eighteen sectors prospected in Azapa Valley (5.6%), while in the valley of Codpa P. cinnamomi was identified in all orchards prospected (100%). Suggesting that in Codpa symptoms in plants are produced by P. cinnamomi, and in the valley of Azapa is rather due to salt toxicity and other soil physicochemical characteristics. The plant pathogen was isolated and inoculated Hass avocado plants, after 30 days affected plants developed symptoms as chlorosis, defoliation, death of branches and tree. The fungus was isolated from inoculated plants and pathogenicity was confirmed. The CO2 assimilation was measured with a LI-COR 6200 in five healthy and five diseased plants obtaining significant differences (p < 0.05) showing that the disease affects photosynthesis.