Poly(ethylene oxide) (PEO) of molecular weight 1000 (PEO1000) containing lithium benzenesulfonate (LiBs) (PEO1000/LiBs), PEO derivatives having benzenesulfonate groups on both chain ends (PEO1000-(BSLi)(2)), or 1-ethyl-2,3-dimethylimidazolium bromide (ImB), were each blended with natural rubber (NR). The ionic conductivity was measured from AC impedance values. The ionic conductivity of the mixture of NR and PEO1000/LiBs (40 wt%) was about 10(-6) S cm(-1) at 50 degrees C; this mixture retained rubbery physical characteristics. At NR content of 10 wt%, the ionic conductivity of the mixture (NR/PEO1000/LiBs) was 2.7 x 10(-5) S cm(-1) at 50 degrees C, approximately 10 times higher than that of the bulk PEO/LiBs mixture. For mixtures of NR and PEO1000-(BSLi)(2), no improvement in ionic conductivity by mixing was found. The ionic conductivity of the mixture of NR and ImB was about 10 times higher than for the bulk of PEO1000-(BSLi)(2) at a NR content of 10 wt%. We propose that the ionic conductivity of the mixture increases when an ion conducting matrix containing simple salt is added. On the other hand, the DSC curve for NR/PEO derivatives showed two T(g)s based on the separate components, suggesting phase separation of the PEO derivative in the NR phase.