The aim of this study was to evaluate the relationship between phoria and asthenopia in adults in the Gyeonggi area. We examined the corrected visual acuity, corrected refractive error, phoria and fusional reserve of 80 healthy myopes aged from 17 to 34 years old who had no strabismus, no ocular and physical diseases. We evaluated the occurrence of asthenopia according to phoria and fusional reserve. 52 out of 80 subjects which exophoria was 56.3% and esophoria was 43.7% made a complaint against asthenopia. The subjects who had exophoria of 0-6Δ in the range of a normal state was 18.5%, while the subjects who had exophoria of 7Δ or more in the range of abnormal state was 81.5%. Reducing fusional reserve was associated with increasing phoria. The subjects who had the fusional reserve two times or more than phoria were 28.5%, and twice or under were 71.5%. The asthenopia complaint persons who had the fusional reserve two times or more than phoria were 32.9%. And the asthenopia no complaint persons who had fusional reserve two times or under comparing to phoria were 67.1%. We found a relationship between asthenopia and fusional reserve of phoria and considered that fusional reserve must be examined when we prescribe for a patient with phoria.