N‐Phenyl maleimide (N‐PMI) was successfully polymerized by divalent rare‐earth complexes (ArO)2Sm(THF)4 (ArO = 2,6‐di‐tert‐butyl‐4‐methyl phenoxo‐; THF = tetrahydrofuran) and (Ar′O)2Ln(THF)3 (Ar′O = 2,6‐di‐tert‐butyl phenoxo‐; Ln = Sm, Yb, or Eu). The central metals greatly affected the reactivity, and the reactivity order was Sm(II) > Yb(II) > Eu(II). The activity of (Ar′O)2Sm(THF)3 was higher than that of (ArO)2Sm(THF)4. The polymerization yields were higher in THF than in other solvents, and the maximum yields were obtained around 25 °C. A proposed mechanism is discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3966–3972, 2005