The researcher used a two- group Pre- test/ Post- Test Quasi- experimental Design to determine the perceived effectiveness of modular approach in teaching Technical Writing among Second year Bachelor of Science in Criminology students of Isabela State University- Cauayan, specifically, it sought to determine the profile of the respondents in terms of age, sex, and type of school graduated from; the academic performance of the students in Technical Writing; the significant difference in the academic performance of the students in the two groups and the reactions of the students on the use of the module in terms of content, organization, label, presentation of concepts, and exercises. The results show that most of the respondents of the study (70 or 83.3%) were aged 17-18; most of them were 52 (61.9%) males and most of them 83 (98.8%) graduated in a public school; and there is a significant difference between the pre- test and post-test achievement scores of students and the students’ who were taught without module got a higher pre- test mean score than that of the students with module. The students with module (experimental group) got a higher post- test mean score than that of the students without module (control group), thus implies that the use of learning modules enhanced the learning of the students and that modular instruction is better than the traditional method of teaching and there is no significant difference between the scores of with module (experimental group) and without module (control group) students thus affirms that the effectiveness of the modular instructional materials cannot be totally attributed to the module: however, when tested, it manifested a significantly different performance among those students and that the use of module is as effective as the usual traditional lecture discussion method. The result also shows that the students perceived that the use of the Technical Writing Module is said to be very effective as it with regards to content, organization, label, presentation of concepts, and exercises and that instructional modules are primary vehicles for delivering content knowledge to students. Based on the findings, it was concluded that aside from the module itself, there are other factors like the teacher factor, and the groupings of the students that could contribute to the high performance of students in Technical Report Writing, instructional modules are primary vehicles for delivering content knowledge to students and the use of instructional modules greatly enhance learning.