An anaerobic fluidized bed reactor (110 L AnFBR) which kitchen waste (KW) was fed as the major substrate and different weight fractions of napiergrass dregs as the supplemental ones for bio-hydrogenation at long hydraulic retention time of 7.3 days was established. Two types of microorganisms could be distinguished by their life surroundings in the microbial community of the AnFBR: one is suspended growth, the other is attached growth. In order to evaluate the biohydrogen potential and kinetic characteristics of the two microbial growths in the AnFBR, a series of biodegradation batch experiments were conducted as the biochemical hydrogen potential test. The suspended microbe had obvious bio-hydrogen production after 3.6 h of lag phase, and the maximum specific hydrogen production rate achieved at 2.65 mmol/g-VSS-hr; the attached microbe stayed longer lag phase about 20 h and the maximum specific hydrogen production rate reached up to 1.06 mmol/g-VSS-hr. The metabolism study was investigated with volatile fatty acids conversion with initial, middle and final constitutes. The huge amount of lactic acid degradation of suspended growth (about 6000 mg/L degradation) displayed a special phenomenon in fermentative hydrogen production. Scanning electron microscope (SEM) was used to observe the morphology of two cultures. We also performed a terminal restriction fragment length polymorphism (T-RFLP) analysis for the diverse microbial identification. Crown Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.