The aim of this study was to compare the proteolytic activity by incubating whole ovine casein with 6 industrial (liquid and paste) and two traditional (paste) rennet preparations from calf, lamb and kid. Casein hydrolysate was analysed by pH 8.6 urea-PAGE analysis and immunoblotting using polyclonal antibodies against αs1 and β-casein (CN). The degradation patterns showed that αs1-CN was hydrolysed more quickly than β-CN giving rise to αs1-I casein. The highest degree of proteolysis was observed in 3 types of industrial rennet, two from lamb, either liquid or paste, and one liquid from calf. Rennet from kid (industrial or traditional/liquid or paste) showed the lowest proteolytic activity. The pepsin content was very different among the tested rennet samples, probably explaining the difference in proteolytic activity.