The main objective of this study was to evaluate the suitability of F&M-C256 (spirulina) biomass in a vegetal soybean drink or in water, as substrate for lactic acid fermentation by the probiotic bacterium ATCC 8014 (LAB8014) and to evaluate the fermented products in terms of bacteria content and organic acids content, biochemical composition, total phenolics, and phycocyanin content, digestibility, and antioxidant activity. After 72 h of fermentation, a bacterial concentration of about 10.5 log CFU mL in the broths containing the soybean drink + spirulina + LAB8014 (SD + S + LAB8014) or water + spirulina + LAB8014 (W + S + LAB8014) was found. Lactic acid concentration reached similar values (about 1.7 g L) in the two broths, while a different acetic acid concentration between SD + S + LAB8014 and W + S + LAB8014 broths was observed (7.7 and 4.1 g L, respectively). biomass was shown to be a suitable substrate for LAB8014 growth. After fermentation, both broths contained a high protein content (>50%). In both broths, total phenolics, and antioxidant activity increased after fermentation (+35, +20, and +93% on average, respectively), while phycocyanin content decreased (-40% on average). Digestibility of W + S + LAB8014 broth statistically improved after fermentation. This study highlights the potential of F&M-C256 biomass as a substrate for the production of new functional lactose-free beverages.