The experiments were conducted to study the changes of the growth hormones, free amino acids,nucleic acids and suger contents of peanut plants after being inoculated with M. arenaria. The results showed that the activity of cytokinin (CTK) and abscisic acid (ABA), the content of indole acetic acid(IAA) in the root and leaves of infected plants increased, and that the content of gibberellic acid (GA3) decreased. The contents of methionin(Met) in the root-knots and the healthy roots of infected Plants were 7. 83 and 6. 43 ug/g in fresh-weight respectively, while that of uninfected plants was zero.The contents of cysteine, lysine, arginin and reducing sugars in the roots of infected plants increased,while the contents of proline, threonine, total sugars and disreducing sugers decreased. The content of Pro in the leaves of uninfected plants was 106.18ug/g in fresh-weight, and that of infected plants was zero.The contents of Thr, glycine(Gly), alanin(Ala), histidine(His), Arg, RNA, total sugars, disreducing sugers and total free amino acids in the leaves of infected plants were significantly lower than those of uninfected plants, while the contents of DNA and phenylalanine(Phe) in the leaves of infected plants were bigger than those of uninfected plants. Ih the same infected plants,the contents of DNA, RNA, valine,Phe and Lys in root-knots were bigger than those of healthy roots, while the content of His of root-knot was lower.