The thermal stability of most nitrile hydratases (NHase) is poor, which has been enhanced to some extent by molecular modifications in several specific regions of the C-terminal domain (C-domain) of beta subunit of NHase. Since the C-domain could be present as a naturally separate domain in a few NHases, the whole C-domain is proposed to be related to the NHase stability. The chimeric NHase (SBpNHase) from the thermal-sensitive BpNHase (NHase from Bordetella petrii) and the relatively thermal-stable PtNHase (NHase from Pseudonocardia thermophila) was constructed by swapping the corresponding C-domains. After 30 min incubation at 50 A degrees C, the original BpNHase nearly lost its activity, while the SBpNHase retained 50 % residual activity, compared with the melting temperature (Tm) (50 A degrees C) of the original BpNHase, that of the SBpNHase was 55 A degrees C. The SBpNHase with higher thermal stability would be useful for the thermal stability enhancement of NHase and for the understanding of the relationship between the stability of NHase and its structure.