Samarium(II) complexes or Samarium(II) complexes/n-hexylamine systems were found to be efficient catalysts for cyclotrimerization of arylnitriles. A variety of nitriles can be converted into the corresponding substituted-s-triazines under mild conditions in good to high yields by using samarium(II) complexes/n-hexylamine as catalysts. The same reaction catalyzed by samarium(II) complexes alone gives s-triazines in moderate yields. A variety of nitriles can be converted into corresponding substituted -s-triazines under mild conditions in good to high yields by using samarium (II) complexes / n-hexylamine as catalysts. The same reaction catalyzed by samarium (II) complexes alone gives s-triazines in moderate yields.