Seaweeds are ecologically important and have many applications economically. Inorganic carbon, nitrogen and phosphorus are the main elements needed for photosynthesis and growth of seaweed. Different concentrations of urea and phosphate as fertilizers with the ratio of 1:10 urea to phosphate (P: N = treatment one = 0.2: 2, treatment two = 0.4: 4, treatment three = 6: 0.6 and treatment four = 0.8: 8 mg/l) made treatments and compared to control (without nutrient, as fifth treatment), and their effects on growth of red macro algae, Hypnea musciformis were evaluated in triplicates. Algae sampled from the tidal area of the Oman Sea offshore at the time of the maximum tide and cultured to get optimum biomass for running the experiment. The algae were inoculated into experimental units and cultured for 45 days. A transparent plastic tank containing 40 liters of filtered seawater considered as the experimental unit. At the end of the experiment, the highest and lowest daily growth rate recorded in treatments 2 and control at the rates of 3.3±0.04 and 2.19 ± 0.02 g/day, respectively (p <0.05). These rates in third and fourth treatments were 2.87 ± 0.01 and 2.8 ± 0.01 g/day, respectively, and had a significant increase on growth of algae in comparison to the control (p <0.05). The results indicated that the concentrations of urea and phosphate rates and their ratios in the medium affecting on growth of this alga under outdoor conditions, and at the concentration of 0.4: 4 mg/l and ratio of 1/10 of phosphate to urea algae had the highest growth.