Loranthus grewinkii is a damaging species that is a type of leafy species and inhabits on trees of Zagros forests. This plant in order to provide some of the needed nutrient elements for photosynthesis, it needs its host plant to obtain the water and nutrients. For that reason, they cause changes in biochemical compositions in their host trees. In this research, the effect of Loranthus grewinkii Boiss & Buhse was investigated on organic compounds such as total tannin, total phenol, dense tannin, flavonoids, protein, total sugars, insoluble sugar and proline in Amygdalus haussknechtii Bornm in Southern Zagros forests, Khoram Abad, Iran. The results showed that the total phenol, dense tannin, total tannin, flavonoids and proline in the leaf of the infected individuals were significantly higher than the healthy wild almond (P≤ 0. 05 and P≤ 0. 01). Also, the results showed that sugar content, soluble sugar and protein in healthy individuals were more than the infected individuals to Loranthus grewinkii (P≤ 0. 05, P≤ 0. 01). It is seemed, increasing secondary compounds such as total phenol, dense tannin, total tannin, flavonoid, and proline due to disease occurs in tree to make efforts in orderto increase tolerance to the disease. Therefore, due to the activity of the semi-parasitic plant on these trees, the drying phenomenon is observed on the crown or branches of wild almond trees, so it can be used in the cleaning practice to prevent the prevalence and spread of Loranthus grewinkii in the Southern Zagros region, especially, Lorestan province.