The aim of this study was to determine the appropriate dosage of NPK fertilizer (16-16-8) for the growth of Dunaliella sp. Two separate experiments were conducted in a controlled temperature (24 ± 2.0 °C) room. Microalgae were inoculated in 8 L jars at 25‰, and initial cell density was inoculated at 1 × 106 cells/mL. In the first experiment, NPK (N:P ratio of 1:1) was added to microalgae culture medium, with N concentrations of 8, 16, and 24 mg/L. The results showed that the highest cell density was obtained with 4.7 × 106 cells/mL on day 11 with the 16 mg/L treatment. In the second study, microalgae were cultured with different ratios of N:P—from 1:1 to 15:1—in which the final N concentration in the culture medium was 16 mg/L. The results showed that the cell density was highest at 5.72 × 106 cells/mL in the N:P treatment ratio of 9:1 on day 9, and the dry weight of biomass reached 0.15 g/L on day 7. Overall, the results of this study indicated that NPK can be used to culture Dunaliella sp., but it is necessary to adjust the N:P ratio to 9:1 in order to obtain the highest growth of the cell population.