This study was designed to investigate the effect of  magnetic water technique on growth performance, feed utilization, water quality parameters and some blood parameters of sex reversed (all-male) Nile tilapia (Oreochromis niloticus) fry. Fry were randomly distributed in three experimental groups reared in glass aquaria. The experiment was based on two levels of stocking density [low level 7 fry/aquarium ( 80 fry /m³) and high level 14 fry/aquarium (160 fry /m³)].The same levels were treated with magnetic water at 0.7 Tesla compared with the control groups ordinary water (0 Tesla) and each group was triplicated, with 0.3g / fry an average initial weight. Experimental fish were fed on commercial diet (31.71% protein and 4170.7 Kcal GE/kg diet). At the end of the experiment, the results indicated that growth performance and feed utilization improved significantly (P>0.01) in magnetic water treatment compared to the control groups with high and low stocking densities. The present study recorded that NH₄, NO₃, NO₂ and DO in magnetic water treatment with high and low stocking densities improved significantly (P>0.01) in comparison with the control groups. While there were no significant differences (P>0.05) in pH. As for blood parameters, there were no significant (P<0.01) differences in them between high and low stocking densities. Results indicated that fish reared in magnetic water treatment improved significantly (P>0.01) compared to those in the control groups in high and low densities. In short, applying magnetic water on aquaculture definitely on Nile tilapia farming improves growth performance.