Abstract: 2009 marks the 100th anniversary of the first description of Pneumocystis，an organism that was initially classified as a protozoan and later in 1988，was phylogenetically reclassified in the fungal kingdom. The organism was ignored for its first 50 years but that has subsequently been recognized as an important pathogen in immunocompromised patients，especially patients with acquired immune deficiency syndrome（AIDS）. This paper reviewed recent progress on the molecular biology，involving in the life cycle and metabolism of the organism.

Key words: Pneumocystis, Life cycle, Metabolism, Molecular biology