The use of antimicrobial growth promoters (AGPs) is under debate in many regions worldwide while some countries (e.g. in EU) have already banned these compounds in poultry diets. The use of therapeutic antibiotics is still in the broiler industry worldwide and although they are essential to maintain animal welfare and to treat chickens from diseases, these compounds are also too often used in a prophylactic manner (Van Immerseel, 2017). In order to improve the immunity and feed utilise of livestock and poultry: research into environmentally friendly feed additives has become one of the main challenges of animal husbandry in the 21st century (Wang, 2017). It is generally accepted that shifts in the intestinal microbiota composition may be the result of dietary changes, such as the addition of cereal fibers (Torok, 2011). In broiler chickens, feed additives, including prebiotics, are widely used to improve gut health and to stimulate performance (De Maesschalck, 2015). Generally, dietary fiber in feedstuff is indigestible for the host but the microbes can use it as energy source. The main precursors of bacterial fermentation in the gastrointestinal tract are different digestible carbohydrates or different non-digestible polysaccharides like the soluble arabinoxylan and beta-glucan of cereal grains. Butyrate, among other short–chain fatty acids, are end products of bacterial fermentation and has several beneficial effects on the host (Hamer, 2008). Increasing the amount of butyric acid in the gut may result in improved gut structure, absorption of nutrients and even improved production traits (Schneeman, 2002). Wheat bran is a cheap fiber source and it contains fiber mainly in the form of arabinoxylan (Stevenson, 2012). Beside its effect on microbial fermentation, arabinoxylan has also been shown to activate a macrophage cell line in the broiler intestine and thus decrease the enteric pathogen colonization (Zhang et al., 2004). An in vivo experiment was conducted to study the effects of xylooligosaccharide, arabinoxylooligosaccharide and soluble arabynoxilan on several groups of gut bacteria of chickens (Courtin, 2008). All treatment groups showed an increase in the number of caecal bifidobacteria after 2 weeks of feeding (P < 0.05), while the treatments did not impact numbers of Enterobacteriaceae and aerobic lactobacilli in the caeca relative to the control. Prebiotic dietary fibers are known to improve the gastrointestinal health of both humans and animals in many different ways. They can increase the bulking capacity, improve transit times, and depending on the fiber, even stimulate the growth and activity of resident beneficial bacteria (Vermeulen, 2018). The aim of this study was to investigate the effect of wheat bran supplementation on the caecal microbiota composition of broiler chickens.