Olive cake, sometimes also called spent olive, is a low-energy nutrition source. It possesses various biological properties that are antioxidant, anti-inflammatory, antimicrobial, and antiviral in property due to its rich polyphenolic compound content. Mucins can be found in the composition of the mucus that cover the surface of the gastrointestinal tract. Feed additives can influence the mucin composition, as well as the height and width of the villi, which are biological appendages tasked to increase the absorption surface in the small intestinal mucosa. The aim of the present study was to determine the histology of the small intestine in Japanese quails fed with olive cake. In the study, mixed-sex quails fed with rations containing different amounts of olive cake were used as the live material. Morphological measurements, Alcian blue/periodic acid–Schiff, and aldehyde fuchsin/Alcian blue histochemical stains were performed on stomach and small intestine tissues taken from quails. Significant increases in villus height, villus width, and crypt depth in duodenum, jejunum, and ileal tissues were determined in control and experimental groups. The increase in crypt depth was greatest in the ileum. In the jejunal tissue, it was determined that the width of the villus decreased in groups 1 and 2 but increased in group 3. In the histochemical evaluation, it was determined that sulphate mucins were intense in the proventriculus, while carboxylic mucins were intense in all three parts of the small intestine. Considering the physiological functions of mucins, olive cake is thought to play an important role in the protection of the mucosa in quails.