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The effect of different levels of nitrogen fertilization on the susceptibility to peach constriction canker, caused by Phomopsis amygdali, was studied on a peach orchard of Rich Lady cultivar, from March 2005 to April 2008. Four different nitrogen levels were used: without nitrogen, 50 kg N ha-1, 100 kg N ha-1, and 200 kg N ha-1. Plant inoculations with P. amygdali were carried out in November. The canker length at the inoculation sites was measured between January and March of the following year and used as a susceptibility assessment. Twenty-five leaves per tree were sampled, in June of each year, to obtain an early diagnosis of the nutritional status of the plants. After three years, the plants with the lowest fertilization level showed 3.2% of nitrogen leaf content and those with the highest fertilization showed 3.9%, indicating a small variability in leaf nitrogen content. A positive correlation was found between nitrogen and sulphur and a negative correlation between nitrogen and magnesium. The highest nitrogen fertilization enhanced susceptibility to P. amygdali, which was to a great extent determined by rainfall.