A 3 × 2 factorial experiment was conducted to investigate the effect of thymol + carvacrol (0, 100 and 200 mg/kg) on ileal microbial population and jejuna and ileal histomorphology of broilers fed Carboxy Methyl Cellulose (CMC: 0 and 2%) containing diet. Each of the 6 dietary treatments was replicated 5 times with 12 chicks each from 0 to 42 days of age. There was no interaction effect of CMC and thymol + carvacrol in any measured parameters. At d 42, the ileal population of lactobacilli and Bifidobacteria were greatest (P<0.05) in birds fed 200 mg/kg thymol + carvacrol but 100 mg/kg of additive had no significant difference with two others treatment. The E. coli population was significantly decreased in birds fed 100 and 200 mg/kg thymol + carvacrol. Supplementation of diet with CMC enhanced (P<0.05) ileal count of E. coli and reduced ileal counts of Lactobacilli and Bifidobacteria as compared to those in chicks fed control diet. Data showed that supplementation of diet with CMC decreased (P<0.05) intestinal histomorphology including jejunal and ileal villus height (VH), villus height to crypt depth (VH:CD) and increased jejunal and ileal villus width (VW), crypt depth (CD) at 21 and 42 days of age as compared to those in chicks fed control diet. Inclusion of 100 and 200 mg/kg thymol + carvacrol improved VH, villus surface (VS), VH:CD and muscular layer (MSL) of jejunum at 21 and 42 days of age and also increased ileal VH, VH:CD, MSL and GC at d 21 and MSL and GC at 42 days of age. Supplementation of diet with CMC decreased (P<0.05) jejunal histomorphology including VH, VH:CD and increased (P<0.05) VW and CD at 21 and 42 days of age as compared to those in chicks fed control diet. At d 21, dietary CMC decreased (P<0.05) VH and in-creased (P<0.05) VW but it did not affect the rest of ileal histomorphological parameters. At d 42, CMC supplementation significantly affected some ileal histomorphological parameters in terms of increasing VW and CD and decreasing VH and VH:CD but the other parameters were not influenced by CMC.

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