A 24-day feeding trial was conducted to assess the effect of feeding four levels of activated charcoal (0.0, 0.33, 0.67 and 1.00 g/kg of body weight) on intake of honey mesquite leaves (Prosopis glandulosa Torr.) by 20 wether lambs (36.6 ± 0.6 kg) that were randomly assigned to treatments. Lambs were fed low quality Sudan-grass hay at 2.0% of body weight and 80 g of molasses during a 7 day adaption period followed by 16-day feeding trial where lambs were fed 1.9% of body weight of same hay and 80 g of molasses mixed with assigned levels of charcoal. During the feeding trial, lambs had ad libitum access to honey mesquite leaves that had been previously harvested, frozen, and thawed immediately before feeding. No differences (P = 0.52) in day-to-day intake of mesquite leaves were detected among treatments. However, lambs consumed more mesquite leaves as the feeding trial progressed (P < 0.001). Mean intake of mesquite leaves were 20.7 ± 3.7, 23.8 ± 3.8, 20.2 ± 3.7, and 27.3 ± 3.7 g/day for the 0.0, 0.33, 0.67 and 1.0 levels of charcoal, respectively. During the last 8 days of the study, consumption of mesquite leaves varied greatly among lambs, ranging from 1.4 to 7.4% of their diet. No differences were detected in hay intake (P = 0.23) and lamb weight gain (P = 0.58) among treatments. Future studies examining consumption of honey mesquite leaves by sheep should consider potential variation in intake among individual animals.