Deviation from optimum percentage (DOP) can be used as an efficient method to interpret the results of plant analysis and the nutritional requirements of agricultural and horticultural crops. To determine the DOP norms and evaluation nutritional status of watermelon, leaf samples were collected from 150 fields of watermelon in west Azerbaijan; and N, P, K, Ca, Mg, Fe, Mn, Zn, Cu and B were determined. The fields were divided into high-yielding (23% of fields, ³ 40.5 ton ha-1) and low-yielding (77% of fields;<40.5 ton ha-1) subgroup and DOP norms were calculated using standard DOP procedure. The optimum concentration of nutrients in leaves of watermelon were obtained as follows: for nitrogen (%2.8), phosphorus (%0.25), potassium (%2.4), calcium (%1) and magnesium %0.47), iron (106 mg kg-1) manganese (83 mg kg-1), zinc (45 mg kg-1), copper (15 mg kg-1) and boron (30 mg kg-1) Among macronutrients, nitrogen and potassium had highest negative indices in 95% and 93% of the studied fields, respectively and among micronutrients, zinc and iron were in 84% and 72% as well. Based on DOP indices, the order of plant nutrients requirement were determined as N>K>Mg>P>Ca for macronutrients and as Zn>Fe>B>Cu>Mn for micronutrients. Plants have high nutritional balance index (NBI) indicating relatively imbalance of absorbed nutrients by watermelon and imbalance fertilizer application in the studied fields.