This study was carried out during 2010/2011growth season on four olive (Olea europaea L.) varieties: Picual, Aggizi, Mission and Koronieki, grown in calcareous soil at the Horticultural farm of El-Nubariya Agricultural Research Station, Ministry of Agriculture and Land Reclamation Egypt. The experimental of design was in a split-split design (two levels of water regime, four cultivars, six treatments and three replicates). The total numbers of experimental plots used were 144 trees. The main treatments included full and half irrigation water (FIW or HIW) of water requirement (ETpan), the sub-main treatments were the four olive varieties, and the Sub-sub main treatments included NPK fertilizers (100, 75, and 50% dose) with effective microorganisms (E.M.) or humic acid (H.A.). The objectives of this study were to investigate the response of four olive varieties to variations in the quantity of irrigation water and NPK fertilizers rates in the presence with H.A. or E.M. The obtained results showed positive significant effects due to FIW or HIW, 75 % NPK +EM or 50 % NPK +EM on fruit weight of Picual and Aggizi,while all treatments showed positive significant effects on increasing fruit weight of Mission. However, Koronieki showed no significant response with all treatments. The oil contents in fruits of Picual, Aggizi, Mission and Koronieki showed significant response to 100 % NPK, 75 % NPK +EM, or 75 % NPK +HA treatment under FIW regime. The highest significant chlorophyll contents in leaves of all olive varieties were obtained by FIW with 75 % NPK +EM and 75 % NPK +HA. The N, P and K contents in leaves of the four olive varieties significantly increased as a result of applying all treatments under FIW or HIW regime. In addition, all treatments increased significantly the levels of total N, available P and available K in the soil and also soil respiration as a result of the all treatments with FIW or HIW regime.