In radio, spokesperson credibility is a resource that can improve the effectiveness of a message, and its analysis requires the study of how voice qualities influence the listener. The aims of this study are to design and test the suitability of a scale of radio spokesperson credibility, and to analyse the effect of the phonoaesthetic function – that is, how a spokesperson’s gender, vocal pitch, accent and their interactions affect their credibility. We conducted a 2 × 2 × 2 experimental design via eight radio programmes in which we inserted a radio spot as stimulus material. The hypotheses were tested on a sample of 987 Spanish radio listeners, and the advertised service was blood donation. The results allowed the validation of a scale of spokesperson credibility, traditionally used in audiovisual media, formed by three dimensions (attractiveness, expertise and trustworthiness), and provide several implications for the selection of a spokesperson for radio.