Subject-verb agreement (SVA) is a core element of English grammar, yet it poses persistent challenges for Libyan EFL learners. This study investigates the types and causes of SVA errors among second-year students at Omar Al-Mukhtar University, Al-Beida. A quantitative case study design was adopted to investigate subject-verb agreement errors among second-year English language students at Omar Al-Mukhtar University.Data were collected using a 30-item grammar test and a 16-item Likert-scale questionnaire, allowing for statistical analysis of both grammatical performance and learner perceptions. Test items targeted compound subjects, quantifiers, collective nouns, and indefinite pronouns, while errors were classified as intralingual, interlingual, or developmental. Findings revealed that intralingual errors were the most prevalent (particularly overgeneralization and simplification), followed by interlingual errors influenced by Arabic, and fewer developmental errors. The most frequent mistakes occurred with compound subjects and quantifiers. Questionnaire data showed that students attributed their difficulties mainly to L1 interference, limited exposure to authentic English input, and insufficient instructional strategies.These findings align with prior studies but highlight the value of integrating learner perceptions into error analysis. The study concludes that improving SVA accuracy requires explicit instruction, contextualized practice, and systematic corrective feedback. It recommends targeted pedagogical interventions to address recurring error patterns and enhance grammar teaching in Libyan EFL contexts................. Keywords:.............. Subject-Verb Agreement, Error Analysis, Intralingual Errors, Interlingual Errors, Developmental Errors, Learner Perception, EFL