Objective To determine the effect of soybean protein on growth of jejunal mucosa. Method Seventeen goat lambs at 7d of age were randomly allocated into control (casein group, n=9) and experimental group (soybean group, n=8). All lambs were fed milk mixture containing either casein or soybean protein (replaced 30% of casein). The lambs were slaughtered after 5 w and the tissues of jejunum were sampled to determine the villus morphology. The mucosa was collected for analysis of protein, nucleic acid content and the activities of alkaline phosphatase (ALP). Results The soybean administration induced villus atrophy. Protein content of mucosa tend to decrease both in proximal (127.2?4.6 vs 143.6?7.3 mg/g mucosa,P=0.07) and medial jejunum(111.2?6.3 vs 132.7?8.5 mg/g mucosa,P=0.06). In soybean group the activity of AP was lower(P