Making spelling errors is one of the common issues faced by learners in any language as Second Language (SL) at the early stage of learning. This study investigated the spelling errors in the writings of undergraduate B.A. English students, University of Bisha, Al-Namas, Saudi Arabia. The study explored the spelling errors’ phenomenon with relation to the phonological syllable structure of words where the spelling errors were classified into three categories of words, (1) mono-syllabic, (2) di-syllabic, and (3) tri-syllabic and complex syllabic words. The researcher analyzed the spelling errors with relation to the sounds/phonemes positions in each syllable, (a) onset position, (b) nucleus position, and (c) coda position spelling errors. The results showed that Arabic-speaking learners made more spelling errors in tri-syllabic and complex syllabic words compared to the spelling errors in mono-syllabic words. The results explored that learners made more spelling errors in the nucleus position with 54.85% and fewer errors in the coda position 36.40%. Interestingly learners made fewer errors than the other groups with 8.75%. This suggested that English vowels, being in the nucleus position, are a more problematic position for Arab learners than consonants. The omission and the substitution spelling errors were more frequent and high compared to other categories. The study explored that the spelling errors are attributed to the different orthographical and morpho-phonological systems of L1 and L2 including the letter-to-sound correspondence and sound-to-letter correspondence, homophones, silent letters. The study concluded with some solutions to help learners avoid the spelling errors such as the importance of the phonological awareness of ESL.