This experiment was carried out to investigate the effect of diet containing herbal blend (HB) of turmeric (Curcuma longa), scent leaf (Ocimum gratissimum), and moringa leaf (Morinda lucida) supplemented with or without L-arginine (L-Arg) on growth performance, intestinal morphology, and caecal microflora of guinea fowls. Three hundred and sixty 28-day-old male guinea fowls were randomly allotted in a completely randomized design to six treatment groups of sixty birds; each treatment group consisted of six replicates of ten birds each. Dietary treatments were laid out in a 3 × 2 factorial arrangement of the basal diet (control), diet containing enrofloxacin (1 g/kg), HB (1 g/kg diet), and each supplemented with or without L-Arg at 1 g/kg. Notwithstanding dietary supplementation with L-Arg, guinea fowls fed the diets with HB, and their counterparts fed the diets with antibiotics had similar weight gain during the growing period. Dietary L-Arg supplementation with HB increased (p<0.05) feed intake. Feed conversion ratio (p<0.05) was improved in guinea fowls fed the diets with HB and their counterparts fed with antibiotic supplemented or not with L-Arg. L-Arg supplementation of the diet with HB resulted in the longest (p<0.05) duodenal villi height and the shortest (p<0.05) duodenal apical width in young turkeys. The caeca content of growing guinea fowls fed the diet with HB supplemented with L-Arg had the least (p<0.05) Clostridium count and the highest (p<0.05) Lactobaccillus count. In conclusion, guinea fowls fed the diet with HB supplemented or not with L-Arg had similar growth performance with those fed with an antibiotic. L-Arg supplementation of the diet with HB resulted in increased caecal Lactobacillus counts of growing birds.