The aim of this study was to examine the effects of herbal essential oil mixture on intestinal mucosal development, weights of the internal organs, carcass characteristics, and growth performance of quail (Coturnix coturnix japonica). A total of 276 quails that were 1 day old were studied. The quails were weighed and divided into 3 groups, each with 4 replicates, consisting of a control, antibiotic (avilamycin 10 mg/kg diet), and the essential oil mixture (EOM) at 48 mg/kg diet. Supplementation with EOM and antibiotic significantly increased goblet cell size and goblet cell number on day 38. Villi height, villi width, and crypt depth were not affected by any treatment. Quails receiving the diet containing EOM and antibiotic were significantly heavier than those fed the control diet on days 28 and 38. No significant effects of the dietary treatments on feed intake were observed. Moreover, addition of EOM and antibiotic to the quail diet resulted in a significantly better feed conversion ratio than that of the control on days 28 and 38. No differences were observed for carcass yield or liver, gizzard, and small intestine weights. Beneficial effects of the EOM were observed in goblet cells of the intestinal mucosa.