<P><B>Abstract</B></P> <P>This study assessed the impact of swine manure (SM) dilution ratio on the microalgal biomass cultivation and further tested for biohydrogen production efficiency from the mixed microalgal biomass. At first, various solid/liquid (S/L) ratio of the SM ranged from 2.5 to 10 g/L was prepared as a nutrient medium for the algal biomass cultivation without addition of the external nutrient sources over a period of 18 d. The peak biomass concentration of 2.57 ± 0.03 g/L was obtained under the initial S/L loading rates of 5 g/L. Further, the cultivated biomass was subjected to two-step (ultrasonication + enzymatic) pretreatment and evaluated for biohydrogen production potential. Results showed that the variable amount of hydrogen production was observed with different S/L ratio of the SM. The peak hydrogen yield of 116 ± 6 mL/g TS<SUB>added</SUB> was observed at the 5 g/L grown SM mixed algal biomass.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Dilution ratio of swine manure concentration affects the microalgae growth. </LI> <LI> Peak microalgae biomass production was obtained as 2.57 g/L. </LI> <LI> Ultrasonication + enzyme pretreatment can be a viable approach for H<SUB>2</SUB> fermentation. </LI> <LI> Peak hydrogen yield of 116 mL/g microalgae biomass was achieved. </LI> </UL> </P>