A new scheme is proposed for concatenative speech synthesis to improve the segment selection procedure by minimizing acoustic distortions between the selected segment and the desired spectrum for the target. The spectral pro-totypicality of a segment, the spectral difference between the source and target contexts, the degradation resulting from concatenation of phonemes, and the acoustic continuity between the concatenated segments are all considered as measures. A search method for selecting segments from a large speech database is also described. In this method, a three-step optimization is used for distortion minimization. A perceptual test shows that contextual spectral difference and acoustic continuity at the segment boundary are important measures for improving the quality of synthesized speech.