A process for the preparation of gabapentin starting from gabapentin hydrochloride, which comprises the following steps: preparing a gabapentin hydrochloride aqueous solution; adjusting the pH of the solution to or about to gabapentin isoelectric point by addition of a basic compound comprising a monovalent anion; diafiltering the solution through a membrane highly selective for organic compounds with molecular weight higher than 150 and poorly selective for inorganic monovalent ions, to separate the solution into an aqueous permeate containing chloride ions and a retentate containing unsalified gabapentin substantially free from chloride ions; concentrating the retentate by increasing the pressure exerted on the membrane to obtain a concentration of unsalified gabapentin in the retentate not lower than 5%; evaporating the retentate under reduced pressure and at T.degree.<35.degree.; precipitating gabapentin by addition of an alcohol.