Maritime pine is extensively used in south-western Europe for lignocellulose production. Increasing demand for wood from this pine species requires efficient production of improved varieties and this is currently achieved only through seed orchards management. As in most long-lived tree species, variety design and deployment would greatly beneficiate from setting up an efficient vegetative propagation system of selected seed resources. Somatic embryogenesis is a promising clonal propagation system in most conifers and significant progress has been made in recent years for maritime pine (reviewed in Klimaszewska et al. 2007). However the « true » maturity of harvested cotyledonary somatic embryos (SE) is still a debatable question. Cotyledonary somatic embryos are currently selected at the end of the maturation phase based on morphological criteria. Embryo maturation is a crucial step giving rise to the establishment of reserve compounds including specific storage proteins (Teyssier et al., 2011) that will ensure optimal germination and subsequent in situ plantlet development. A 2D-PAGE proteomic approach has been developed at INRA of Orléans to define the protein status of developing SE in reference with zygotic embryos (ZE). We aimed at contributing for a better understanding of the processes acting during the maturation phase of SE (part 1). As a first step towards this goal this work is presenting water content and percentage of dry mass in maturing SE vs. ZE (part 2) and our first results in proteomic analysis of SE development (part 3). This new knowledge is expected to ultimately results in refining our current methodology for practical application of somatic embryogenesis in maritime pine.