Pronunciation has been an important topic in English education, especially for English as a Foreign Language (EFL) learners and teachers. Based on the bilingual education policy in Taiwan (The Bilingual Nation 2030 policy, 2019), one of the objectives is to improve English communication skills. Pronunciation has been one of the key factors for effective communication. Most EFL studies (Hismanoglu, 2009; Bui, T. S., 2016; Ercan & Kunt, 2019) found many EFL learners face difficulties and make errors in pronouncing interdental sound /ð / and /θ/, however, few studies examined the interdental pronunciation errors specifically with a detailed analysis. With a classroom-based approach, this research aims to employ a qualitative analysis to investigate Taiwanese elementary school EFL learners and examine their pronunciation errors of the interdental sounds, including /ð / and /θ/ in English, providing a systematic analysis and phonetic-based learning strategies for elementary school teachers to solve the pronunciation problems of interdental sounds. The research questions are as follows: (1) What errors of Taiwan elementary school EFL learners would occur in pronouncing /ð / and /θ/ in English? (2)What is the pattern of these pronunciation errors when they appear in different positions of a word? (3)What are the causes of the problems in pronouncing /ð/ and /θ/? What is the solution for Taiwanese EFL teachers and learners? This study will conduct a survey to investigate Taiwanese elementary EFL learners’ pronunciation performances with the focus on interdental sound through recordings, interviews, and questionnaires to collect and analyze the general pattern and frequency of the pronunciation errors. Our classroom-based research findings would help to categorize the interdental pronunciation errors and pinpoint pronouncing errors of the interdental sounds in different positions (beginning, middle, or end) of a word, and propose learning strategies for English teachers and learners to solve the pronunciation problems with phonetic-based effectively.