This study reports the dominant linguistic errors that occur in the written productions of Arba Minch University (hereafter AMU) students. A sample of paragraphs was collected for two years from students ranging from freshmen to graduating level. The sampled compositions were then coded, described, and explained using error analysis method. Both quantitative and qualitative analyses showed that almost all components of the English language (such as orthography, morphology, syntax, mechanics, and semantics) in learners' compositions have been affected by the errors. On the basis of surface structures affected by the errors, the following kinds of errors have been identified: addition of an auxiliary (*I was read by gass light), omission of a verb (*Sex before marriage ^ many disadvantages), misformation in word class (*riskable for risky) and misordering of major constituents in utterances (*I joined in 2003 Arba minch university). The study also identified two causes which triggered learners' errors: intralingual and interlingual. The majority of the errors, however, attributed to intralingual causes, which mainly resulted from the lack of full mastery on the basics of the English language.