The study emphasized on the effects of brassin-like substance (BS) on fruit size of Arabica coffee (Coffea arabica L.). The experiment designed in randomized complete block design (RCBD) with 5 treatments and 4 replications (one tree per replication). The trees were sprayed with BS at the concentrations of 0, 0.1, 0.5, 1.0 and 1.5 mgL-1 every four weeks after fruit set until harvesting stage (10 spraying times). The results showed that the coffee in BS 1.5 mgL-1 treatment gave the largest fruit and bean sizes. It also gave the heaviest fruit and green beans. All of BS concentrations did not affect percentage of bean dry weight. The highest percentage of the best grade (A grade) coffee beans was found in BS 1.0 and 1.5 mgL-1 treatments. BS 0.5, 1.0 and 1.5 mgL-1 could hasten fruit ripening. However, BS 0.5, 1.0 and 1.5 mgL-1 decreased the percentage of fruit set and yield.