Self-incompatibility (SI) system is a genetic barrier that prevents self-fertilization and promotes cross-pollination among different S genotypes. In many of these species, SI is controlled by a single genetic locus known as S locus, which prevents the fertilization by pollen with same locus. S RNases are the products of the S-locus expressed in the stylar tissue of Fuji Apple with gametophytic self-incompatibility system. This study investigated the various types of chemicals in order to select more effective inhibitors and activators. The effect on the inhibition of S RNase of Fuji apples was investigated $in$ $vitro$. The result showed that the enzyme activity was reduced 24.3% by Iron(II) Sulfate, significantly. $In$ $vitro$ studies of pollen growth tube showed that pollen tube growth had a higher germination rate (90%) in 10% Sucrose than in 2% sucrose extension medium. Data on the fruit set of apples treated with inhibitor and activator. Double application of $A^+$(Apple Plus, ISTECH Co. Ltd.,)+Vitamin B6 had the highest central fruit set as 86.1%(Andong). One time application of $A^{++}$Vitamin B1 in Yeongju obtained the highest central fruit set (91.9%).