The possibility of utilizing blended wastewaters from different streams was investigated for cost-efficient microalgal cultivation. The influent of a domestic wastewater treatment plant and the liquid fertilizer from a swine wastewater treatment plant were selected as water- and nutrient-source wastewaters, respectively. The growth of Micractinium inermum NLP-F014 in the blended wastewater medium without any pretreatment was comparable to that in Bold’s Basal Medium. The optimum blending ratio of 5–15% (vv−1) facilitated biomass production up to 5.7g-dry cell weight (DCW) L−1, and the maximum biomass productivity (1.03g-DCWL−1d−1) was achieved after three days of cultivation. Nutrient depletion induced lipid accumulation in the cell up to 39.1% (ww−1) and the maximum lipid productivity was 0.19g-FAMEL−1d−1. These results suggest that blending water- and nutrient-source wastewaters at a proper ratio without pretreatment can significantly cut costs in microalgae cultivation for biodiesel production.