This paper proposes a novel voice conversion method by frequency warping.The frequency warp-ing function is generated based on mapping formants of the source speaker and the target speaker.In addi-tion to frequency warping,fundamental frequency adjustment,spectral envelope equalization,breathiness addition,and duration modification are also used to improve the similarity to the target speaker.The pro-posed voice conversion method needs only a very small amount of training data for generating the warping function,thereby greatly facilitating its application.Systems based on the proposed method were used for the 2007 TC-STAR intra-lingual voice conversion evaluation for English and Spanish and a cross-lingual voice conversion evaluation for Spanish.The evaluation results show that the proposed method can achieve a much better quality of converted speech than other methods as well as a good balance between quality and similarity.The IBM1 system was ranked No.1 for English evaluation and No.2 for Spanish evaluation.Evaluation results also show that the proposed method is a convenient and competitive method for cross-lingual voice conversion tasks.