A series of batch culture experiments of two marine microalgae Dunaliella salina Teodoresco and Nannochloropsis salina Hibberd was conducted at various humic acid (HA) concentrations (0.0, 0.1, 0.2, 0.3, 0.4, 0.5 mgL^-1) to evaluate the stimulatory potential of HA on the growth (expressed as a biomass concentration), pigment production (chlorophyll a and carotenoids) and C/N ratio. The impact of HA on the proximate composition (moisture, ashes,dietary fiber, crude lipid, available carbohydrates, crude protein and the energy content) was also considered. Results demonstrated a highly significant positive effect of HA on growth, pigment production and proximate analysis (P≤ 0.01). The response of both investigated microalgae to HA show optima in the range of concentration studied, which makes it a low cost-high yield investment.However, C/N ratio in D. salina showed a gradual decrease upon addition of HA. On the other hand a slight increase in the ratio was observed in N. salina.