The effects of the application of the chemical thinner Armothin® on fruit set, yield and quality of Japanese plum (Prunus salicina Lindl.) cv. ‘Fortune’ were studied during two seasons in Central Chile (34.56°S, 71.5°W). Trees were sprayed with Armothin® at 0.5%, 1% and 2% concentrations. All thinning treatments reduced the fruit set and fruitlet number (fruitlets/50 cm of branch). Armothin® at 2% conc. was the most aggressive treatment, drastically reducing the fruit set from 85.9% and 82.9% of the control and crop load to unprofitable levels during both seasons. Chemical thinning treatments at the two lowest concentrations (0.5 and 1%) did not significantly alter the crop load compared with the unsprayed control during both study seasons. Thinning costs were reduced (Armothin® 0.5%, 25.0% and 21.5% of the control treatment and Armothin® 1%, 24.6% and 24.1% of the control, during the first and second season, respectively). In general, chemical thinning increased the fruit size and total soluble solids content (TSS). Taking into account the ef- fects on thinning, crop load, fruit quality and thinning costs, Armothin® 1% and Armothin® 0.5% are the most advantageous treatments in the case of this study.