Conventional automatic English evaluation systems used only acoustic features extracted from an input speech. However, not only the speaker' s pronunciation ability but also the difficulty of the sentences affect the pronunciation score. In this paper, we referred to the difficulty of sentences as 'speakability.' Analysis of variance revealed that sentence speakability was effective in the evaluation as well as the speaker s pronunciation ability. We also showed that the number of phonemes in a sentence and word familiarity were useful as features to estimate sentence speakability. Finally, we carried out the multivariate regression analysis to estimate the sentence speakability score from these features, and the correlation coefficient was 0.41.