Three strains of Dunaliella salina (I, G and A) were cultivated under the climatic conditions of Iran, in open ponds to compare the β-carotene production and the specific rate of growth. The experiments were accomplished in two separate stages. In the first stage, the cells were grown in ponds on nutrient-rich medium containing 2 M NaCl to obtain the necessary biomass. In the second stage, cells were stressed on nutrient-poor medium containing 2.5 M NaCl for β-carotene induction. The results showed that the specific growth rate of strain I was the highest during the first stage, whereas during the second stage, the growth rates of three strains were approximately the same. The overall results indicated that strain G had the highest potential for β-carotene accumulation of the strains tested and hence it was concluded that this strain is more suitable for outdoor cultivation under the climatic conditions of Iran than the other two.