Abstract: The mites occurring on button mushroom (Agaricus bisporus) in Karaj region of Iran were studied. Seventeen species belonging to three orders and nine families of mycophagus, predaceous and saprophagus mites were found, during a survey conducted from the spring 2004 to summer of 2006. The mites species were: Macrocheles glaber (Müller), Macrocheles merdarius (Berlese), Macrocheles subbadius (Berlese), Parasitus coleoptratorum* (Linnaeus), Parasitus fimetorum (Berlese), Parasitus mammillatus (Berlese), Sancassania rodionovi Zachvatkin, Tyrophagus putrescentiae (Schrank), Uroobovella fimicola (Berlese), Ameroseius fungicolus* Masan, Pediculaster kneeboni* (Wicht), Pediculaster flechtmanni*(Wicht), Scutacarus longitarsus (Berlese), Dendrolaelaps multidentatus* Masan, Arctoseius cetratus (Sellnick), Lasioseius sugawarai* Ehara and  Ameroseius plumigera Oudemans. Six of them are new for the Iranian acaro-fauna that are indicated by asterisk. Twelve species are recorded for the first time from mushrooms.

Key words: Mite fauna, Agaricus bisporus, new records, Iran