The predatory mite Amblyseius cucumeris (Oudemans) (Acari: Phytoseiidae) was studied in the laboratory and in the field in order to evaluate its potential as a biocontrol agent against the citrus red mite Panonychus citri (McGregor), a pest of citrus in Fujian Province, China. When fed P. citrus females and eggs, A. cucumeris completed its development from the egg to adult in about a week at 24–28°C. Females fed on prey eggs more than on other stages and produced 2–3 eggs per day, with a maximum of 4. The number of P. citri females consumed by A. cucumeris females per day, and the number of eggs produced by these females increased significantly with the number of prey females per leaf. However, when there were fewer than 5 prey females per leaf, the searching efficiency of the predators was so low that most (86%) did not lay any eggs. A positive linear relationship was found between the number of prey consumed and the number of eggs produced. When a fixed number of prey (30 females) was available, the predator population increased faster and reduced prey populations faster when predator:prey ratio increased from 1:30 to 9:30. Releases of predators onto potted citrus seedlings showed that predator females released at predator:prey ratios as low as 1:54–58 provided control of the citrus mite in five weeks. Field trials showed that a single preventive release of A. cucumeris using a controlled release system provided adequate control of citrus red mite and also significantly reduced the rate of black fruits. Biological control cost 1/3 less than conventional chemical control.