Russian knapweed (Acroptilon repens L.) is a perennial weed of Aceraceae that is becoming a dominant weed in suitable conditions. In order to find an ecological non-chemical approach for controlling Russian knapweed and studying the possibility of using flower-eater mite (Aceria acroptiloni Shevchenko & Kacalev) (Acari: Eriophyidae), a series of studies including field survey and field experiments were conducted in North Khorasan province, Agricultural Research Station of Shirvan College during spring 2010. Preliminary studies included collecting, identifying and screening of insects as biocontrol agents for Russian knapweed were carried out. In field survey studies, contaminated natural regions by flower-eater mite were recognized. At the end of growing season, 20 health and infested plants were selected and their height, flower number, shoot fresh weight and shoot dry weight were measured afterwards. In the field experiment, 40 similar plants with about one meter away from each other were selected. In addition, 40 plants (20 infected and 20 healthy plants) were transplanted to the pots, and then planted in a land with a distance of about 100 cm. After establishment, control plants were sprayed with an acaricide 20 shoots each that used as ‘control’ and 20 shoots that infested with the mite were randomly selected. Russian knapweed shoots infested with the mite Aceria acroptiloni in a natural infestation were collected and observed under the binocular for the presence of the mite. The infested shoots were put in small vials filled with water, and transfer one shoot beside each of the 20 shoots that were selected for mite infestation. Mite infestation of the test shoots after two weeks was checked and in case the test shoots did not show signs of mite attack after four weeks, plants were infested again. As soon as the Russian knapweed leaves start wilting (when the green colour disappears), all 40 shoots were cut at the ground level. Each shoot put in a separate envelope, and the envelope labeled. In the laboratory, shoot height, fresh shoot weight, dry shoot weight, number of flower heads, numbers of seeds were recorded. The results showed that the mite did not feed from all plants except on Russian knapweed. Application of mite reduced the number of flowers by 68% in natural conditions. In the field conditions, it could reduce the number of flowers by 59% in the nature plants and 11% in transplanted plants. Since this mite was able to reduce vegetative and reproductive organs of Russian knapweed, it could be considered as a potential promising biological control agent for using in ecological agriculture.