Flaxseed (Linum usitatissinum L.) oil is an important source of α-linolenic (C18:3 ω-3), this polyunsaturated fatty acid is well known for its nutritional role in human and animal diet. Understanding storage lipid biosynthesis in developing flaxseed embryos can lead to an increase in seed yield. While a tremendous amount of work has been done on different plant species to highlight their metabolism during embryos development, flaxseed metabolic flux analysis is still lacking. In this context, we have developed an in vitro cultured developing embryos of flaxseed and determined net fluxes by performing three complementary parallel labeling experiments with 13C-labeled glucose and glutamine. Metabolic fluxes were estimated by computer- aided modeling of the central metabolic network including 11 cofactors of 118 reactions of the central metabolism, 12 pseudo fluxes. A focus on lipid storage biosynthesis and the associated pathways was done in comparison with rapeseed, arabidopsis, maize and sunflower embryos. In our conditions, glucose was the main source of carbone of flaxseed embryos, leading to the conversion of phosphoenolpyruvate to pyruvate. The oxidative pentose phosphate pathway (OPPP) was identified as the producer of NADPH for fatty acid biosynthesis. Overall, the use of 13C-metabolic flux analysis provided new insight into flaxseed embryos metabolic processes involved in storage lipids biosynthesis. The elucidation of the metabolic network of this important crop plant reinforces the relevance of the application of this technique to the analysis of complex plant metabolic systems.