Soybean lecithin (SL) is commonly used as a nutritional supplement in animal diets. This study investigated the effects of SL on feed intake, ruminal fermentation, rumen microbial populations, digestive enzyme activities, and apparent nutrient digestibility in sheep. The feeding trial involved four Chinese Merino rams fitted with permanent rumen fistulae in a 4 × 4 Latin square design, fed a basal diet supplemented with 0, 10, 20, and 40 g/day of SL for 22 days. SL addition significantly increased the intake of ether extract (EE), phosphorus, and the apparent digestibility of EE and acid detergent fibre (ADF) (P < 0.05). It also influenced the total counts of bacteria and fungi (P < 0.05), while protozoal populations remained unaffected (P > 0.05). The concentrations of total volatile fatty acids and ammonia nitrogen decreased significantly (P < 0.05), whereas the activities of carboxymethyl cellulase and filter paper cellulase increased (P <0.05) with rising levels of SL supplementation in sheep rumen fluid. These findings suggest that dietary SL can improve rumen fermentation parameters, stimulate digestive enzyme activity, and increase the apparent digestibility of EE and ADF. The results of this study indicate that 20 g/day is the optimal SL supplementation level in sheep diets.