This study was conducted in nine olive orchards in three villages during 2001-2002 in the Mut district of Mersin province. Pesticides were not used. On olive trees, two eriophyid mite species, Aculus olearius Castagnoli and Aceria oleae (Nalepa) (Acarina: Eriophyidae), were found in the fruit pit of immature fruits. The first species is a new record for Turkey. These species were found together in the same population. Injury levels, damage types and infestation ratios on leaves, inflorescences, buds, flowers and fruits were determined. Damage constituted greenish-yellow spots on the middle and tip sections of old leaves and malformations on the young leaves as a result of feeding of these mites. These pests caused dark green collapsed sections and rust stains on buds, and abnormal shapes and brown split sections on fruits. Three to five over-wintered adults were observed in april (2002) on newly expanded leaves and in the section attached to twig of leaf stalk. There were 20-35 mites in the third week of april and 50-70 mites on buds at the end of april within one colony. In the first week of may, the population density reduced on flowers. At the end of may, population density reached maximum levels and 80-100 mites were observed within one colony. After the first week of june, the population density began to reduce and in the last week mites that migrated from fruits to leaves didn’t form colonies on the leaves. The ratio of leaves showing symptoms of greenish yellow spots and malformation were 24 % and 42 %, respectively. In addition, the ratio of infested fruit was 74 %.