Ungrammaticality is highly observed through incorrect usage of conventions or standards of grammar. Grammar is defined as “the rules that govern how a language’s sentences are formed” (Thornbury, 2000). It is one of the most difficult aspects of a foreign language to master. The main purpose of this action research was to address problems through process-based approach on the ungrammaticality of English language usage on the essays of Grade 11 Electrical Installation and Management Students of Sawata National High School for the first semester of School Year 2016-2017 in order to develop their communicative strategy. This study was anchored to the Theory of Communicative Competence by (Canale & Swain, 1980) which gives more focus on Strategic Competence as one of the components of Communicative competence. Results revealed that the forms of ungrammaticalities observed from the written outputs of the Electrical Installation Management Students (Grade 11) are: Subject-Verb Agreement, Tenses of Verbs, Voices of Verbs, Adverbs and adverbials, prepositions and Prepositional Phrases, Pronoun and Pronoun Antecedent Agreements, Word Choice or Lexical Categorization, Usage of Infinitival Tense Particle “To”, Capitalization and Punctuation Rules, and Spelling. Second, the Process Based Approach is very effective in dealing ungrammaticalities on writing as it is very evident in the progress of written outputs of the students in the process. Hence, it is proven that it is a very effective action to solve the said problem of ungrammaticality and improving the Communicative Strategic Competence of the Students.