The objective of this study was to evaluate the use of oat hulls (OH) to substitute traditional fiber (a mixture of rice hulls and mugwort (RHM) leaf) in the diets of fattening rabbits by examining on its effect on the growth performance, coefficient of total tract apparent digestibility (CTTAD) of nutrients, gastrointestinal tract development, cecum fermentation and carcass traits. A total of 160 mixed sex Hyla commercial meat rabbits (40/treatment) were used to study the effects of including OH in the diet from 30 to 80 days of age. A control diet based on RHM and containing 175.2 g crude fiber and 169.7 g CP/kg was included. Growth performance and CTTAD of nutrients were recorded from day 35 to day 80 and day 74 to day 80, respectively, whereas gastrointestinal tract development, cecum fermentation and carcass traits were determined at day 80. Increasing concentrations of OH in the diet increased average daily feed intake (P=0.0018), but have no effects on average daily gain and feed conversion ratio (P>0.05). Moreover, the 150 g/kg OH diet decreased the relative weight of full cecum and cecal content (P<0.05), but did not affect other gastrointestinal organs. The CTTAD of NDF and gross energy decreased with the inclusion of OH (P<0.05). No effects of CTTAD of ADF, ADL, dry matter, CP and ether extract were observed (P>0.05). The concentrations of total volatile fatty acid, acetic and butyric acids were greater in rabbits fed the lower levels of OH (0 to 100 g/kg) compared with higher rate (150 g/kg; P<0.05). However, the proportions of acetic, propionic and butyric acids were not affected by treatments (P>0.05). Furthermore, no significant effect on the ratios of acetic/(propionic+butyric) was observed (P>0.05). Hot carcass weight, pH (45 min, 24 h), lightness, redness, yellowness, 24-h drip loss of longissimus lumborum muscles were not affected by diet OH (P>0.05). However, dressing out percentage increased with higher (150 g/kg) inclusion of OH. It is concluded that OH can be included in rabbit diets at levels up to 100 g/kg, but negative effect on digestion and performance were observed with the increasing of OH (150 g/kg).