This study investigates the effectiveness of Computer-Based Instruction (CBI) in teaching Biology to 7th graders of a secondary night school in Cebu City, Philippines. A pretest and posttest quasi-experimental design with a control group was utilized to two groups of students, of which one was exposed to CBI and the other to the conventional lecture method (CLM). An Instructional Materials Motivation Survey (IMMS) was used to assess its motivational characteristics. Data gathered were analyzed using descriptive statistics, frequency count and percentage, mean and standard deviation, t-test. Findings revealed that both groups had Fairly Satisfactory performance in the pretest, which implies that the students had low knowledge on the topic. The study also found that both groups had significantly increased their performances from the pretests to the posttests, implying the essence of CLM and CBI use. Ultimately, the study revealed that the use of CBI is more effective than CLM, as seen in the enhanced students' performance, signifying the effectiveness of the instruction using a computer in teaching Biology concepts. The students commended the CBI for being a user-friendly, autonomous, self-paced, and selfregulating instructional design that helped them enhance their performance in the least learned competencies. A contextualized CBI in Biology was crafted to serve as a guide for teachers and enable the students to pave the way for the mastery of the different competencies in Biology.