An experimental study was conducted to assess the effect of proteins as air-entraining agents in different binary cementitious systems. More specifically, air-entraining performance, mechanical properties and transport characteristics of cement pastes blended with up to 30 % fly ash and slag and air entrained with different proteins were evaluated. The experimental program included measuring the hydrophobization of the cement matrix, microstructure, compressive strength, water absorption, and electrical resistivity. It was found that the air-entraining performance of proteins in blended cement binders is affected, and the degree of this effect depends primarily on the properties of each protein. There appeared to be a general reduction in air-entrained porosity in the blended systems containing fly ash in most protein cases. Although the overall water absorption did not show a correlation with air-entrained porosity, a softening of the transition point between initial and secondary absorption was observed and attributed to a wider distribution in void sizes in the pastes air entrained with proteins. In addition, the electrical resistivity of the pastes air-entrained with proteins did not demonstrate a strong correlation with air-entrained porosity indicating a complex influence of proteins on pore structure and pore solution chemistry.