This study was carried out at theExperimental Farm of Faculty Agriculture (Saba- Basha), Alexandria University, Egypt, during 2016 and 2017 growing seasons to investigate the response of potato cv. Herms to water stress and organic manure fertilization under drip irrigation system. The experiments were carried out in a split plot design with three replicates. Four irrigation levels (100, 75, 50 and 25% of ET₀) were arranged in main plots and the four organic manures (control, cows, sheep, and chicken) were arranged in sub plots. The results indicated that, all vegetative growth parameters (plant height, shoot fresh and dry weights, leaf area index, and total chlorophyll) significantly affected by irrigation level and organic manure fertilization in which 100% of ET₀ and chicken manure gave the highest values. Also, the yield and its components gradually increased with increasing water supply up to 100% compared with other treatments during 2016 and 2017 seasons, such as, (tuber length, tuber diameter, average of the tuber weight, specific gravity, tuber dry weight, total tubers yield, % of marketable tubers/plant  and weight of unmarketable tubers/plant, respectively). Also, increasing soil moisture contents from 75% to 100% caused a significant increase in the concentrations of N, P, K, reducing sugars, non-reducing sugars and total sugars in tubers, in both seasons. Also, a significant increase of tubers starch percentage, compared to the other treatment was observed during both seasons. On the other hand, that application of chicken manure produced the highest values of all yield and its components and chemical composition of potato plants during both seasons compared with the other organic treatments. As general, irrigation of potato at 100% of ET₀ and fertilizing with chicken manure lead to the highest values of vegetative growth and yield, thus it is recommended to use these treatments as agricultural practices in similar areas for potato production. The findings in this study strongly recommend that irrigation at 100% of reference evapotranspiration would be advantage if the farmer's target is to maximize tuber yield. But if the target is to put more area into production under limited water supply, irrigation at 75% of reference evapotranspiration in potato may be feasible.