Abstract: The objective of this study was to evaluate the effect of the amount of Perilla frutescens seed (PFS) in the diet on the serum biochemical parameters, rumen fermentation characteristics, apparent nutrient digestibility, and growth performance of Hu sheep. Sixty male Hu lambs aged 2 months and weighing on average (23.02±1.36) kg were randomly divided into four groups and fed on diets containing varying proportions of PFS: 0% (control), 5% (5%PFS), 10% (10%PFS) and 15% (15%PFS) for 70 days. At 21 days before the end of the feeding experiment, four lambs were randomly selected from each experimental group for a 7-day digestion and metabolism experiment. At the end of the feeding period, lambs were weighed to calculate average daily gain (ADG). Blood and rumen fluid samples were collected for analysis. Volatile fatty acids (VFA), ammonia nitrogen (NH₃-N), total protein (TP), urea nitrogen (UN), glucose (Glu), growth hormone (GH), and insulin-like growth factors 1 (IGF-1) were quantified in the samples using gas chromatography, colorimetric, automatic biochemical analyzer, and ELISA methods. The results showed that the amount of PFS did not significantly affect growth performance (dry matter intake, ADG, and feed/gain ratio), blood biochemical indices (TP, UN, Glu, GH and IGF-1), rumen pH, or the concentrations of acetic acid, propionic acid, and total VFA (P>0.05). With increasing dietary PFS, the concentrations of acetic acid, butyric acid, and total VFA tended to decrease, whereas the concentration of propionic acid tended to increase. Compared with the control group, the 15%PFS group showed significantly decreased NH₃-N content and acetate∶propionate ratio (P<0.01) in the rumen fluid. The amount of PFS did not affect the apparent digestibility of ether extract (EE) and neutral detergent fiber (NDF) (P>0.05). However, the apparent digestibility of dry matter (DM), organic matter (OM), and NDF decreased with increasing amounts of PFS in the diet. The apparent digestibility of DM and OM was lower in the 15%PFS group than in the other groups (P<0.05). Compared with the control group, the 10%PFS group showed significantly increased apparent digestibility of crude protein (CP) (P<0.01), while the 15%PFS group showed a significant decrease in this parameter (P<0.01). In conclusion, 10% PFS in the diet is the appropriate level of supplementation for Hu sheep.