Castor-bean cake, a by-product of biodiesel industry, has been used as fertilizer and as parasitic control in soil. However, its protein could be extracted and used to produce biodegradable materials, enhancing the value of this raw material. The most common process for protein extraction uses alkaline solubilisation, which is also the main treatment against ricin, the toxic protein of castor-bean cake. Thus, the aim of this research was to study the effect of alkaline agents (NaOH or KOH) and pH (10, 11 or 12) on the protein extract composition. Dry matter, proteins, ash, lipid and non-protein nitrogen and also macro minerals and trace elements were determined. In general, the increase in pH do not influenced neither the dry matter content (~93.3 %) nor the non-protein nitrogen content, but influenced the protein content as consequence of the pH increasing. Similar behaviour was observed for ash content due to increasing the amount of both alkaline. The freeze-dried protein extracts presented lower lipids content (~0.8 %), regardless of both alkaline agent and pH values. The nitrogen was the most abundant mineral (10 %) in the protein extracts for all the extraction conditions, while the other macro minerals contents were lower than 1.0 %. With respect to the trace elements, iron was the most abundant independently of the alkaline agent used. We can concluded that the protein extracts are protein concentrates, and the protein content increased with increasing extraction pH. The alkaline agent NaOH was slightly more effective for protein extraction.