Abstract: The adducts MDI-RA were firstly synthesized from liquified diphenylmethane diisocyanate(MDI) and ricinoleic acid(RA). Then esterification reaction between ethylene diglycidyl ether and MDI-RA was carried out for the preparation of the castor oil based epoxy active intermediates(RAE). Finally, the chain reaction of RAE with diethylenetriamine(DETA) and glycidol was performed to obtained the waterborne epoxy curing agents based on castor oil. By this way, two kinds of target products(RAWCA-1 and RAWCA-2)were obtained from feeding ratio of the n(MDI):n(RA) of 1:3 and 1:4, respectively. The chemical structures of the intermediates and the target products were confirmed by Fourier transform infrared spectroscopy(FT-IR), proton nuclear magnetic resonance(¹H NMR) and gel permeation chromatography(GPC). The results showed that the structure parameters of target products were basically agreed with the designed molecular structure and the M_n and M_w of target products were 1 832 g/mol and 1 983 g/mol. The property study showed that the target products could emulsify liquid epoxy resin E-51. The properties of the two-component film obtained from the curing reaction of RAWCA-1 and liquid epoxy resin E-51 were as follows:flexibility 1 mm, pencil hardness 3H, impact resistance 50 kg/cm, good water resistance, which could meet a requirement with commercial waterborne epoxy curing agent products.