Correct spelling is often emphasised in an EFL (English as a foreign language) classroom in Taiwan despite the fact that there are many reasons behind learners' spelling mistakes. By analysing fifty-seven texts from a dictation test and a composition competition in a private comprehensive high school, this study discusses EFL students' spelling problems with reference to the differences between Chinese and English writing systems. Several types of spelling errors were identified, including sound-based errors, visual/graphic errors, morphological errors, splits, slips and punctuation errors. Towards the end of the paper, some suggestions are drawn for English spelling instruction based on the error analysis.