Activated carbon fibers (ACFs) were firstly applied as fluidized solid carrier to immobilize photo-fermentative bacteria (PFB) for H-2 production in batch culture. The observations by scanning electronic microscopy (SEM) demonstrated the close interaction between ACFs and PFB. The amount of immobilized bacteria and the performance of H-2 production were strongly affected by specific surface area, length and amount of ACFs, respectively. Large specific surface area provided more surface attachment sites and more PFB were immobilized. ACFs with proper length avoided intertwining with each other and better fluidized during reactor operation. Excessive amount of ACFs not only limited the light conversion efficiency, but also increased biofilm detachment, resulting in low H-2 yield. The maximum yield (3.08 mol H-2 mol(-1) acetate) and rate (32.85 ml l(-1) h(-1)) of H-2 production were obtained, using specific surface area (1500 m(2) g (1)), length (1 mm) and amount (0.8 g l(-1)) of ACFs. Compared with the conventional solid carriers, ACFs were effective solid carriers to immobilize PFB for improving H-2 production, due to bacteria immobilized on the external surface of fluidized ACFs and formed a layer of dense biofilm. (C) 2012 Elsevier Ltd. All rights reserved.