Hypothesis: This study demonstrates that tuning the shell thickness of lipid particles can modulate their oxidative stability. We hypothesized that a thick crystallized shell around the incorporated fish oil would improve the oxidative stability due to the reduced diffusion of prooxidants and oxygen. Experiments: We prepared solid lipid nanoparticles (5% w/w lipid phase, 1.5% w/w surfactant, pH 7) by using different ratios of tristearin as carrier lipid and omega-3 fish oil as incorporated liquid lipid stabilized by high- or low-melting lecithin. The physical, polymorphic and oxidative stability of the lipid particles was assessed. Findings: The high-melting lecithin was the key in inducing the formation of a solidified tristearin shell around the lipid particles by interfacial heterogeneous nucleation. Lipid particles containing a higher ratio of tristearin showed a better oxidative stability. The results revealed that a crystallized tristearin layer above 10 nm was required to inhibit oxidation of the incorporated fish oil. This cut-off was shown for lipid particles containing 50-60% fish oil. This research gives important insights into understanding the relation between the thickness of the crystallized shell around the lipid particles and their chemical stability. (C) 2016 Elsevier Inc. All rights reserved.