Fourty growing APRI male rabbits at the age of 5 weeks old were used to investigate the impact of partial replacement of concentrate feed mixture (CFM) CP by different levels of hydroponic barley (HB) on rabbits performance, digestibility, feeding value, some blood constituents and caecum microbial count. The changes in chemical composition of HB during 6, 7 and 8 days of growth period was also studied. Rabbits were randomly divided into four experimental groups (10 rabbits in each) and were housed in individual cages provided with continuous feeders and automatic water nipples during the experimental period (5 – 12 week of age). The first group was fed pelleted CFM diet with 16% CP (control, D1), while the 2^nd, 3^rd and 4^th groups were fed the control diet but 20, 40 and 60% of CP was replaced by HB (D2, D3 and D4, respectively) in a feeding trial which lasted for 7 weeks. At the end of the feeding trial, four digestibility trials were carried out on three rabbits of each treatment. Animals were fed the same tested diet as that in feeding trial. Three rabbits of each treatment were slaughtered at the end of digestibility trials. The main results generally showed that there was a tendency for gradual decreases in DM and NFE content, but increases in Ash, EE, CP and CF content by advancing age of sprouting. Rabbits fed D2 recorded the highest significantly (P < 0.05) values of digestion coefficients of CP and CF, while the lowest significantly (P < 0.05) values were recorded with rabbits fed D4 diet. There were positive significant (P<0.05) effect of feeding HB at levels of 20 and 40 % on concentrations of blood total protein, albumin and glucose. Rabbits fed HB diets (D2, D3 and D4) had significantly (P < 0.05) higher total viable count of bacteria in caecum compared with those fed the control diet without HB (D1). It may be concluded that replacing of HB at the rate of 20 or 40 % of CFM protein in growing rabbit diets had beneficial effects on most criteria studied. Higher level (60% of HB) used herein in rabbit diets is not recommended since it negatively affected nutrients digestibility and feeding values of tested diets.