According to FAO, Iran is one of the most important apple producers in the world, with annual average production of two million tons. Furthermore, based on FAO reports, apple export by the country has had an increasing trend during recent years. To preserve this trend and raise the income, using mechanical equipments for harvesting, traorting, handling, sorting, and packing processes of apples is required. Nevertheless, these unit operations are performed manually in our country. On the other hand, apple is too delicate and preserving its quality during these processes is essential. So researchers are endeavoring to find strategies to design these systems and decrease damages in both harvesting and post harvesting, by studying the causes of mechanical damages. Bruising is the most important mechanical damage to apples. The majority of such damages is caused by dynamic forces resulting from impacts. Therefore, it is justifiable to investigate fruit behavior under impact. In this study, an impact test device specialized for free fall (drop) was fabricated. The experiments were conducted in two ways. In the first one, after measuring the apple mass, it was dropped from different heights on an aluminum plate equipped with a load cell and then the force-time curve was recorded. In the second method, halved apples were stabilized on a rigid steel plate, and then spherical impactors with different masses dropped on them from different heights. The two methods were applied on two varieties, Jonagold and Fuji, harvested at three different dates. The flesh stiffness near the impact area was measured for all apples using penetration test with a universal tension and compression testing machine. The radius of curvature of the apple surface at the impact area was measured by a curvature meter before impact test. Bruise volume and area of apples were measured 24 hours after impact test by measuring their dimensions. To study the effect of variety and harvest date on bruising, the results were analyzed using a factorial experiment in a completely randomized design. Analysis of variance and the mean comparison indicated that the effects of the variety, harvest date, and their interaction on bruise volume and area were significant ( P 0.05). The results illustrated that Jonagold variety was more sensitive to damages caused by impact than Fuji ones. With delayed in harvesting time, the average bruise volume and area were generally increased. Afterward, the bruising threshold was obtained as the allowable falling height and initial energy of impact producing bruise area of less than 100 mm 2 . The allowable falling height was calculated for the first, second and third harvesting times which were respectively 9.6, 4.3 and 2.7 cm for Jonagold apple and 6.0, 5.1 and 8.5 cm for Fuji apple. Furtheremore, the allowable initial energy of impact was obtained for the first, second and third harvesting times which were respectively 100.1, 46.9, and 23.1 mJ for Jonagold apple and 61.5, 49.1, and 70.2 mJ for Fuji apple. Finally, several multiple linear regression models were developed to predict bruise volume and bruise area of both Jonagold and Fuji in collision with flat plate and spherical aluminum impactor. Keywords: Apple, Jonagold, Fuji, mechanical damage, bruising, impact, stiffness, bruise threshold