Recently, oil-in-water Pickering emulsions has attained considerable interest for the purpose of delivering lipophilic bioactive components into water-based food products. These surfactant-free emulsions are stabilized with solid colloidal particles which are an appropriate alternative for low molecular weight surfactant based emulsions due to their superior stability against coalescence and disproportion as a result of the irreversible attachment of the particles at the interface. Using food-grade particles due to their lack of toxicity, biodegradability and the possibility of incorporation in food products without any side effects of synthetic surfactants, has attracted attention. The aim of this study was the fabrication of stable flaxseed oil (FO)-in-water Pickering emulsions stabilized by complex and plant-based flaxseed protein (FP) and the soluble fraction of flaxseed mucilage (SFM) as a delivery system for food products. FO is a lipophilic functional compound which has a limited application in food industry due to its poor water solubility and its susceptibility to oxidation. The extracted SFM and FP were characterized using 1-D 1H and 13C NMR and SDSPAGE, respectively. The effect of pH, total concentration (TC) and FP to SFM ratio on the formation of assemblies was investigated by light scattering, surface charge and optical density measurements. The selected complex particles at pH=3, FP to SFM ratio of 50:50 and TC=0.45 wt% were negatively charged with a zeta potential value of -22.3 mV and the size of 369 nm with the polydispersity index (PDI) of 0.31, which quarantines good physical stability. and had a near neutral wettability. The changes in interfacial tension and FTIR profile of the FP and SFM before and after complexation was also investigated. The selected nanoparticles had the contact angle of 67° which is suitable for the stabilizing of oil-in-water Pickering emulsions. These nano-assemblies were utilized to fabricate Pickering emulsions with different FO content (1, 2.5 and 5 w/v%) and TC= 0.45 wt% and the droplet size during 28 days of storage and accelerated creaming stability of the emulsions was investigated. 2.5 wt% FO emulsion had the smallest initial droplet size (D[4,3 = 8 µm) and creaming velocity (2.9 µm/s). For the sake of comparison polysorbate 80 stabilized emulsions (PS80) as conventional emulsions were also prepared at the same condition. The microstructure of the emulsions was demonstrated utilizing Cryo-SEM and confocal microscopy showing a thick layer of the particles on the oil surface responsible for the stabilization. FO emulsion stabilized by complex bioparticles had a good physical stability during 28 days of storage and against various environmental stress conditions including a wide range of pH (2-9), salt concentration (0-500 mM) and temperature (40, 60 and 80 °C for 30 min) with no sign of instability and oiling-off. The measurements of peroxide value (PV) and thiobarbituric acid (TBA) during 28 days of storage at at 4 °C and 50 °C displayed the increased oxidation by increasing the temperature and storage time. The complex particles as Pickering emulsifiers were successful to depress the FO oxidation. The effect of bioparticle stabilization the digestion fate of FO was also evaluated. Lipid digestion was slower in complex particle stabilized emulsions compared to control FO, FP- and PS80- stabilized emulsions, respectively. This study could open a promising pathway for producing natural and surfactant-free emulsions through Pickering stabilization using plant-based biopolymer particles for protecting and delivery of lipophilic bioactive components. These emulsions are also applicable for designing functional foods with controlled lipid digestion to increase satiety and to reduce the incidence of obesity. Key Words Pickering emulsion, complex nanoparticles, Flaxseed protein, Flaxseed mucilage, Flaxseed oil