This research aims to analyze English as a Foreign Language (EFL) pre-service teachers’ perceptions regarding the didactic component of pronunciation of English fricative phonemes [ð] and [θ]. The participants under study were 93 EFL pre-service teachers from two universities that belong to the public and the private sector in southern Ecuador. An exploratory mixedmethod design involving the administration of an online questionnaire, a diagnostic test and a follow-up interview were used. The results reveal that erroneous pronunciation of pre-service teachers is related especially to the phonetic segments of the English language that do not exist in the repertoire of Ecuadorian Spanish, especially dental fricatives. It was observed that as far as the phoneme th moves from the initial position towards the middle or final positions, the pronunciation gets even inaccurate. This means that Ecuadorian Spanish speakers have a tendency to pronounce the fricative phonemes in the initial position better.