Purpose - The purpose of this paper is to investigate in situ modification of cyclohexanone-formaldehyde resins (CFR) by 4-vinyl aniline (Van). The roles of the reaction temperature, the conductivity, thermal properties, and molecular weight of the product were investigated. CFR was in situ modified with VAn in the presence of sodium hydroxide. Ketonic resin-bound 4-vinyl aniline was synthesised with a one-step method of in situ modification of ketonic resin. The roles of the reaction temperature and the conductivity of the product were investigated.