Proteomics analysis has been performed in leaf tissue from field date palm trees showing the brittle leaf disease (BLD) or maladie des feuilles cassantes, the main causal agent of the date palm decline in south Tunisia. To study the evolution of the disease, proteins from healthy and affected leaves taken at three disease stages (S1, S2 and S3) were trichloroacetic acid acetone extracted and subjected to two-dimensional gel electrophoresis (5-8 pH range). Statistical analysis showed that the protein abundance profile is different enough to differentiate the affected leaves from the healthy ones. Fifty-eight variable spots were successfully identified by matrix-assisted laser desorption ionization time of flight, 60 % of which corresponded to chloroplastic ones being involved in the photosynthesis electronic chain and ATP synthesis, metabolic pathways implicated in the balance of the energy, and proteases. Changes in the proteome start at early disease stage (S1), and are greatest at S2. In addition to the degradation of the ribulose-1.5-bisphosphate carboxylase oxygenase in affected leaflets, proteins belonging to the photosynthesis electronic chain and ATP synthesis decreased following the disease, reinforcing the relationship between BLD and manganese deficiency. The manganese-stabilizing proteins 33 kDa, identified in the present work, can be considered as protein biomarkers of the disease, especially at early disease step.