Photosynthetic unicellular sources contain a large variety of proteins. The types of proteins vary between different microalgae and cyanobacteria. The aim was to study the effect of the variation in proteins and in non-proteinaceous components present in various unicellular protein isolates on their emulsion behavior. Algae soluble protein isolates (ASPIs, 66–77% w/w protein) of Nannochloropsis gaditana, Tetraselmis impellucida and Arthrospira (Spirulina) maxima were studied, using commercially available WPI as a reference (93% w/w protein). All protein isolates could form emulsions stable against creaming (d 3,2 0.2–0.3 μm) at pH 8.0. The amount of each ASPI needed (C cr ; on protein basis) to form these stable emulsions varied between the isolates, but was within the range of proteins from both similar (photosynthetic) sources (algae and sugar beet leaves) and other protein sources (dairy, legume and egg). Minor differences were observed in the pH dependence of flocculation amongst the ASPI stabilized emulsions. For the ASPIs, the expected correlation between interfacial and molecular properties (adsorption rate constant and ζ-potential) and the emulsion behavior (C cr and droplet size as a function of pH) was absent.