Purpose: We investigated effects of ground whole flaxseed supplementation on erythrocyte polyunsaturated fatty acids (PUFAs) and serum biomarkers of inflammation, endothelial dysfunction, oxidative stress, and thrombosis in Chinese with risk factors of metabolic syndrome (MetS). Methods: This study was a secondary analysis of a 12-week, randomized, parallel-group trial in participants screened for MetS. The analysis included only those with 2 or more components of MetS before receiving either lifestyle counseling (LC, n = 90) or LC + 30 g/day flaxseed supplementation (LCF, n = 83). Results: Compared to the LC group, those in the LCF group experienced significant increases in total erythrocyte n-3 PUFAs, α-linolenic acid, eicosapentenoic acid, and docosapentenoic acid (all P < 0.001), while total n-6 PUFAs (P < 0.05) and n-6/n-3 ratio decreased (P < 0.001). Arachidonic acid increased significantly in the LC group (P < 0.001), and serum high-sensitivity C-reactive protein, interleukin-18, soluble intracellular adhesion molecular-1, E-selectin, and plasminogen activator inhibitor-1 declined significantly in both groups (all P < 0.05), but no between-group differences were observed. There was no significant change in serum interleukin-6, tumor necrosis factor-α, soluble vascular adhesion molecular-1, monocyte chemoattractant protein-1, and oxidized low-density lipoprotein in either group. Conclusions: These data suggest that flaxseed supplementation increases erythrocyte n-3 PUFAs, decreases n-6 PUFAs and n-6/n-3 ratio in participants with risk factors of MetS, but has no additional benefits beyond the lifestyle consulting for the multiple biomarkers tested in the current study. © 2012 Springer-Verlag Berlin Heidelberg.