Vocabulary is the most important component of language knowledge; it is one of the best predictors of language performance. This descriptive one-group quasi-experimental action research aimed to determine the effectiveness of Do It Yourself (DIY) Word Notebook in improving the Vocabulary of Grade 10 students of a national high school in Zambales, Philippines. A total of 40 students served as the participants of the study. A pretest/posttest served as the main instrument in gathering data which involved the measurement of the students’ vocabulary skills in terms of Definition, Spelling, Parts of Speech, Synonym, Antonym, and Word usage. Results revealed that before the intervention, the level of vocabulary of the students is Fairly Satisfactory. In particular, the students are Fairly Satisfactory in spelling, word usage and synonym while they Did Not Meet Expectations in parts of speech and definition. After exposure to the intervention, the class improved to Satisfactory based from the post-test mean score of 32.95. In particular, the students are Very Satisfactory in spelling and parts of speech, Satisfactory in definition and synonym, and Fairly Satisfactory in word usage and antonym. It can be concluded that there is a significant difference in the vocabulary of the students before and after the implementation of the DIY Vocabulary Notebook. Likewise, there is a significant difference in the students’ vocabulary when grouped according to language use at home, ethnicity and mother’s highest educational attainment. The use of DIY Vocabulary Notebook is hereby recommended to be used in English classes.