The Fermi surfaces are calculated for PrFe4P12, PrRu4P12 and PrRu4Sb12, by using an FLAPW and the LDA + U method within Im = (3) over bar structure, where Pr3+(4f(2)) is singlet. The result reveals that the instability of the Fermi surfaces is responsible to the structural phase transition observed in PrFe4P12 and PrRu4P12. (C) 2002 Elsevier Science B.V. All rights reserved.