The blotch leafminer Cosmopterix salahinella Chrétien (= C. phragmitidis Amsel) (Lepidoptera: Cosmopterigidae) is a new record pest species on oboe cane, Arundo donax L., plants in Egypt. Samples were collected weekly from oboe cane plants grown in or at the banks of irrigation canals at Al-Aiat in Giza governorate from December 2001 to February 2002 and resumed by November 2002 till January 2003 as well as from August 2003 to January 2004. Aspects of biology, ecology and parasitism were determined. Infestation levels fluctuated greatly (45.7, 4.8 and 33.4% ) were recorded occupied with 116, 100 and 110 mines/100 infested leaves in 2001-2002, 2002-2003 and 2003-2004, respectively. This leafminer had two generations and moths emerged during August-October and February-April. The highest rates of larval and pupal parasitism were 25.6 and 30.8% recorded in 2003-2004 opposed to 11.8 and 7.9 % in 2001-2002 with a general rate about 20% in all seasons. The most abundant species were Pediobius sp. and Brachymeria sp. accounting for about 47 and 50% of the total number of collected larval and pupal parasitoids in this study, respectively.