Résumé : We investigate the nucleosynthesis in the helium flash convective zone, triggered by the hydrogen mixing, for extremely metal-poor stars of low and intermediate mass. Mixed hydrogen is converted into neutron through 12C(p,γ) 13N(e +ν) 13C(α ,n) 16O and the doubly neutron-recycling reactions 12C(n,γ) 13C(α,n) 16O(n,γ) 17O(α,n) 20Ne operate. In addition to oxygen and neon, not only light elements from sodium through phosphorus but also the s-process elements, heavier than iron, are synthesized via successive neutron captures with 20Ne as seeds even in the stars originally devoid of metals. We follow the both the doubly neutron-recycling reactions and the s-process nucleosynthesis up to Pb and Bi by varying model parameters such as the amount of mixed 13C. The resultant abundance patterns is shown to reproduce the observed enhancement not only of oxygen, the light elements but also Sr observed from HE 0107-5240 and HE 1327-2326. © 2006 American Institute of Physics.