Abstract: Esca is a complex disease of special interest and involves several fungi in the trunk of grapevine plants. Symptoms can appear several years after primary infection. The microbial behavior of the fungi involved in the disease remains, however, poorly investigated at the early stage of infection. In this study early colonization behavior of Phaeoacremonium aleophilum was assessed using one gfp transformant on one year-old rooted cuttings of Cabernet Sauvignon. Results showed that the fungus can be present six week post inoculation inside xylem fibers before reaching the lumen of xylem to cause disease with other fungi. Knowledge of the early colonization pattern of one fungus considered as pioneer in esca disease can be of special interest to develop control tools against esca-associated fungi.