a process for the preparation of a single crystal of a biopolymer by growth from a solution , which comprises continuously changing one factor having an influence on the conditions for crystallization of a solution of a biopolymer , fractionating the solution , and independently crystallizing the resultant fractions . the process may be carried out by an apparatus comprising a means for feeding a crystallizing agent solution , a means for feeding a biopolymer solution , a means for producing a series of changes of predetermined crystallization conditions , said means continuously changing at least one factor having an influence on the conditions for crystallization of the biopolymer solution , and means for fractionating the solution and independently crystallizing the resultant fractions .