The hydrogen production of sludge in different seasons was investigated, and the process was carried out for two times, respectively, in 2009 and 2010. The morphological characteristics of the bacteria in the sludge were observed by microscope. The results showed that seasonal climate change had a large influence on the hydrogen yield which showed a periodical change annually. The greatest influence on the hydrogen yield appeared in summer and fall, the second appeared in spring, and in winter the influence was the minimum. The hydrogen production of sludge was related to the local atmospheric temperature, and the annual periodical change of the local atmospheric temperature resulted in the annual periodical change of the hydrogen production. The main hydrogen production bacteria in the sludge was Clostridium perfringens ATCC 13124 (CP), and other non-hydrogen production bacteria such as Enterococcus (E) could depress the hydrogen production of CP. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved