Alkyl methacrylate-maleic anhydride-alkyl methacrylate terpolymers (MR(1)-MA-MR(2)) is one of the widely used cold flow improver. In order to develop more efficient MR(1)-MA-MR(2), it is necessary to study the crystallization behavior of n-alkanes when adding MR(1)-MA-MR(2) into diesel fuel. In this paper, MR(1)-MA-MR(2) is prepared by the reaction of long-chain alkyl methacrylate (MR(1)), maleic anhydride (MA), and short alkyl methacrylate (MR(2)). The diesel fuel before and after adding MR(1)-MA-MR(2) is in situ filtrated at its cold filter plugging point (CFPP) in a manual CFPP apparatus. Extensive measurements of composition variation of n-alkanes are done by gas chromatograph and the results are compared. The experimental results show that after adding MR(1)-MA-MR(2), the concentration distribution of n-alkanes in the filtrate is wide and arranges from 8 to 26, and mainly centralizes from 10 to 19. For the precipitate, the concentration distribution of n-alkanes gets richer in the lighter n-alkanes and poorer in the heavier n-alkanes. The concentration distribution of n-alkanes in the crystal solid shows a decreasing trend, especially with high carbon number n-alkanes (heavier than C(20)). About 60-70% of the residual crystal solid is composed of non-paraffins such as isoparaffin, naphthene and other components. Crystallinities of n-alkanes show a slow decrease trend from C(8) to C(20). When the carbon number n-alkanes are heavier than C(20), the crystallinities of n-alkanes begin to sharply reduce with an increase of carbon number. The largest decline of crystallinity is C(26) n-alkane from 38.39% to 7.90%. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.