Tomato cultivars Blizzard and Liberto were grown hydroponically in a controlled temperature (C.T.) room for 35 days. The objective was to investigate the relationship between phosphorus (P) concentration and acid phosphatase enzyme [EC.184.108.40.206.] (APE) activity in leaves in relation to zinc (Zn) concentration in nutrient solution. Zinc was added at concentrations of 0.01, 0.5, and 5 mg L. The 0.01 and 5 mg L Zn treatments led to a significant reduction in dry matter and total chlorophyll content compared with 0.5 mg L for both cultivars. Zinc concentration was considered inadequate in the leaves of plants subjected to 0.01 mg L Zn, while it was at toxic level in those in the 5 mg L Zn treatment according to values stated for tomato plants. Optimal results for all criteria tested in this experiment were for plants grown in 0.5 mg L Zn treatment. In the leaves of plants grown at 0.01 mg L Zn, APE concentrations were significantly the lowest and concentrations of P were at a toxic level. The APE activity was noticeably higher in the P-deficient plants of both cultivars grown in the solutions with high Zn (5 mg L).