A process to produce protein isolates from oriental mustard ( Brassica juncea ) was developed by modifying a method originally developed for rapeseed. The optimised process consisted of extraction at pH 11, ultrafiltration with concentration factor 4, diafiltration with diavolume 3, and precipitation at pH 5. The process based on defatted oriental mustard seed containing 45-50% protein recovered 81% of the protein in useful products: 47.3% in precipitated protein isolate, 3.8% in soluble protein isolate, and 13% in meal residue. Mass yields were 21.9% in precipitated protein isolate, 2.8% in soluble protein isolate, and 38.4% in meal residue. The losses in the system included ~10% loss of non-protein nitrogen, and <9% loss into permeate and error. The precipitated protein isolate compared favourably with soy protein isolate in typical meat products in terms of colour, texture and flavour. The work confirms that oriental mustard is a potentially useful source for oilseed protein production.