Postharvest diseases cause a great reduction in the quantity and quality of fruits yield. Treatment of tomato fruits with salicylic acid (SA) and Hydrogen peroxide (H₂O₂)  elicitors enhanced the resistance to fruit rot caused by Alternaria solani. Moreover, the treatment decreased the development of post-harvesting fruit rot disease. The treatment with either SA or H₂O₂ individually or in combination on tomato shoots (in farm) decreased the diameter of fruit rotted area, decreased the PG  activity, significantly increased PAL, PPO, POD  enzyme activities and increased PR2  and PR3 genes expression after fruit harvesting. On the other hand, treatment by elicitors after harvesting decreased both diameter of rotten area and decreased PG activity but increased the activity of the PAL, PPO, POD enzymes. Also, the gene expression of PR2 and PR3 genes were high in compared to treatment by elicitors before fruits harvesting. The same observation was obtained by the combination of SA and H₂O_2, diameter rotten area was decreased and the PG as well. Significant incensement in the activity of enzymes PAL, PPO, POD, this combined with high expression of both PR2 and PR3 genes.