This research determined the implication of code switching to the English achievement of the Grade 11 students enrolled in Humanities and Social Sciences strand. Quantitative research design was used to find out the factors, forms, functions, and frequency of the students' code switching, and to correlate the code switching and the students' English achievement. A survey questionnaire was used to gather the needed data and Pearson correlation was used to determine the relationship between the students' code switching and their English achievement. The results of the study showed that the dominant factors or reasons which influence the students' English-Cebuano code switching were loss of words, exposure in English and Cebuano languages, comfort, and lack of awareness on equivalent English terms or phrases. The study found out that the most common form of the students' code switching was extra-sentential or tag switching. Furthermore, the findings showed that the prevalent functions or usage of students' code switching were quotation, addressee specification, interjection, message qualification, personalization, clarification, and facility of expression. Generally, the students rarely code switched and they have very satisfactory English achievement. It was found out that the students' code switching has no significant relationship with their English achievement.