In the Philippines, English grammar proficiency plays a significant role in students' academic success and self-efficacy, yet many students face challenges in mastering this area of the language. This study aimed to examine the relationship between Filipino students' proficiency in English grammar which focused on tenses, subject-verb agreement, and punctuation and their self-efficacy in handling language-related tasks. Correlational and causal research designs were employed. A quantitative approach to gather data from 151 Grade 9 students selected through stratified sampling. The research instruments included a grammar competency test and a 5-point Likert scale self-efficacy survey. Statistical tools such as Mean, Standard Deviation, Pearson Product Moment Correlation Coefficient, and Multiple Linear Regression were used for analysis. Results revealed that student-respondents have Very Satisfactory result in Subject-Verb Agreement but Satisfactory in Tenses and Punctuation. They are undecided in their Self-Efficacy which signifies as Moderately Confident. Subject-Verb Agreement has inverse correlation to students’ self-efficacy. Other grammar competencies are not correlated. And no grammar competencies, included in this study influence students’ self-efficacy. Thus, grammar competency among students does not develop students’ efficacy. There may be other factors which are not included in this study that can improve the self-efficacy of the students. An intervention is introduced in this study to have more focused-on grammar exercises in their curriculum to boost students' efficacy.