Ferulic acid (FA) is a phytochemical with various bioactive properties. It has recently been proposed that due to its phytogenic action it can be used as an alternative growth promoter additive to synthetic compounds. The objective of the present study was to evaluate the growth performance, carcass traits, fiber characterization and skeletal muscle gene expression on hair-lambs supplemented with two doses of FA. Thirty-two male lambs (n = 8 per treatment) were individually housed during a 32 d feeding trial to evaluate the effect of FA (300 and 600 mg d −1 ) or zilpaterol hydrochloride (ZH; 6 mg d −1 ) on growth performance, and then slaughtered to evaluate the effects on carcass traits, and muscle fibers morphometry from Longissimus thoracis (LT) and mRNA abundance of β 2 -adrenergic receptor (β 2 -AR), MHC-I, MHC-IIX and IGF-I genes. FA increased final weight and average daily gain with respect to non-supplemented animals (p ˂ 0.05). The ZH supplementation increased LT muscle area, with respect to FA doses and control (p ˂ 0.05). Cross-sectional area (CSA) of oxidative fibers was larger with FA doses and ZH (p ˂ 0.05). Feeding ZH increased mRNA abundance for β 2 -AR compared to FA and control (p ˂ 0.05), and expression of MHC-I was affected by FA doses and ZH (p ˂ 0.05). Overall, FA supplementation of male hair lambs enhanced productive variables due to skeletal muscle hypertrophy caused by MHC-I up-regulation. Results suggest that FA has the potential like a growth promoter in lambs.