This experiment was conducted to study the effects of flaxseed on serum biochemical indices related to lipoprotein and fat metabolism of meat sheep. Twelve 1-year-old wethers with similar body weight were randomly divided into four groups with three replicates in each group and one sheep per replicate. Sheep in control group were fed a basal diet (without flaxseed), and the flaxseed for sheep in experimental groups were processed under three different modes, which were uncooked grain, saute grain and grounding, respectively. The experiment was consisted of three successive 4×4 Latin square tests, and the supplemental levels of flaxseed were 75, 150 and 225 g/d, respectively. The experiment lasted for 180 days with 60 days and four stages (15 days per stage) in each Latin square test. Lipoprotein metabolism related biochemical indices were detected from venous blood samples which were collected at 1.5,7.0.12.0 and 18.0 hours after feeding on the second day of every formal experiment period of the three Latin square tests, and fat metabolism related biochemical indices were detected in the 225 g/d flaxseed Latin square test. The results showed as follows: 1) compared among different processing modes, serum high density lipoprotein cholesterin (HDLc), low density lipoprotein cholesterin (LDLc) and apolipoproteins A (APO-A) concentrations and HDLc relative content in saute grain group were significantly higher than those in the other groups (P<0.01), and those in uncooked grain and grounding groups were significantly higher than those in control group (P<0.01). With the increase of supplemental level of flaxseed, serum triglyceride (TG), HDLc, LDLc, very low density lipoprotein cholesterin (VLDLc) and APO-A concentrations, and HDLc relative content were all significantly increased (P<0.01). Compared among different time points, serum TG, HDLc, VLDLc, APO-A and apolipoproteins B (APO-B) concentrations, and LDLc and VLDLc relative contents experienced an extent of down-up-down during 1.5 to 18.0 hours after feeding. 2) Compared among different processing modes, serum insulin (INS) concentration and hormone-sensitive triglayceride lipase (HSL) activity in saute grain group were significantly higher than those in the other groups (P<0.01), and those in grinding and uncooked grain groups were significantly higher than those in control group (P<0.01), however, fatty acid synthase (FAS) activity showed a converse tendency; serum 3-hydroxy-3-methylglutaryl-CoA reducase (HMGR) activity in control group was significantly higher than that in the other groups (P<0.01), and that in saute grain and grinding groups was significantly higher than that in uncooked grain group (P<0.01); serum acetyl-CoA carboxylase (ACCase) activity was control group > grinding group > uncooked grain group > saute grain group, differences among groups were significant (P<0.01). Compared among different time points, during 1.5 to 7.0 hours after feeding, serum FAS and ACCase activities in three experimental groups were significantly decreased (P<0.05 or P<0.01), and during 7.0 to 18.0 hours after feeding, they were gradually increased, however, serum HSL activity and INS concentration exhibited a converse tendency; the above indices related to fat metabolism in control group changed on the contrary with experimental groups. In conclusion, flaxseed can strongly improve HDLc nutritional value and weaken positive effects resulting from LDLc on body. At the same time, flaxseed also can improve fat metabolism related serum biochemical indices obviously. Under conditions in the present experiment, the optimal processing mode is saute grain.