The effect of a dietary phytogenic feed additive (PFA) inclusion level in mucin monosaccharide composition, mucosal morphometry and mucus histochemistry along the broiler intestinal tract was studied. Cobb male broilers (n = 525) were allocated into five experimental treatments that, depending on the type of addition in the basal diet (BD), were labeled as follows: C (BD based on maize–soybean meal with no other additions), E1 (80 mg PFA/kg BD), E2 (125 mg PFA/kg BD), E3 (250 mg PFA/kg of BD) and A (2.5 mg avilamycin/kg BD). Samples from duodenum, ileum and cecum of 14- and 42-day-old broilers were collected and analyzed. In 14-day-old broilers, treatments E2 and E3 had higher (P < 0.01) duodenal mannose than treatments C, E1 and A. Ileal mannose was lower (P < 0.05) in treatment C compared with PFA treatments, and ileal galactose (Gal) was higher (P < 0.01) in treatments E2 and E3 compared with C and A. Polynomial contrast analysis with respect to PFA inclusion level showed that in 14-day-old broilers there was a linear increase (P = 0.001) in duodenal mannose and a quadratic effect (P = 0.038) in duodenal N-acetyl-galactosamine with increasing PFA level. Ileal Gal and mannose increased linearly (P = 0.002 and P = 0.012, respectively) with PFA inclusion level. There were no significant differences between treatments in mucin monosaccharide molar ratios of 42-day-old broilers. However, increasing PFA inclusion level resulted in a linear decrease of ileal fucose (P = 0.021) and cecal N-acetylgalactosamine (P = 0.036). Experimental treatments did not differ (P > 0.05) regarding duodenal villus height (Vh), crypt depth (Cd) and Vh/Cd ratio, irrespective of broiler age and the intestinal segment examined. However, increasing dietary PFA inclusion level showed a pattern of linear increase of duodenal Vh/Cd ratio in 14-day-old broilers and ileal Vh in 42-day-old broilers (P = 0.039 and P = 0.039, respectively). Alcian Blue–Periodic Acid-Schiff (pH 2.5) staining of neutral and acidic mucins showed that the staining intensity of mucus layer in villi was fragment (i.e. tip, midsection and base) dependent, whereas in crypts it was dependent both on intestinal segment (i.e. duodenum, ileum and cecum) and fragment. Finally, mucus layer thickness did not differ (P > 0.05) between treatments, yet a pattern of linear increase (P < 0.05) with PFA inclusion level was observed in the duodenum of 42-day-old broilers. In conclusion, the dietary inclusion level of PFA modulated broiler intestinal mucin composition and morphology. Further studies are required to elucidate the physiological implications of such changes in host–microflora interactions.