The process of digesting DNA - Na obtained from f ish spermary of chub mackerel into 5..- Deoxymononucleotides by using 5..- phosphodiesterase f rom Penicillium citrinum, M71 was studied. The 201 .. 8 anion exchange resin was used in the separation. The conditions for setting samples are height of column bed 105mm, diameter of column bed 45mm, sample concentration 213mg..mL- 1 and eluting flow..rate 0. 5mL..cm- 2 ..min - 1 . The results of the separation indicated 5..- deoxymononucleotides components could be fully eluted as a whole peak by the elut ing agent, 0. 005 M HCl and 0. 04M NaCl. And the use of a few modified eluting agent s, i. e. 0. 001 8M HCl, 0. 002 8M HCl, 0. 036M NaCl( pH6. 0) and 0. 005M HCl+ 0. 02M NaCl could bring about perfect and respective elution of dCMP, dAMP, TMP and dGMP.