This study was carried out to investigate the relative effectiveness of Computer-Assisted Instruction on academic achievements, retention and attitude in electrolysis concept among senior secondary school students in Kankia education zone, Katsina State, Nigeria. The study had four research objectives, four research questions and four null hypotheses. A total number of 123 students consisting of 78 males and 45 female selected using Simple random sampling techniques formed the sample of the study. The study adopted the pretest, posttest, and post post-test quasi experimental and control group design. The subjects in the experimental group were taught using Computer-Assisted Instruction (CAI), while the control group was exposed to lecture method for a period of six weeks. Two validated research instruments, with reliability coefficient of 0.9 and 0.7, namely Electrolysis Concept Achievement Test and Students? Attitude towards Electrolysis Concept Questionnaire were used in data collection. Three null hypotheses were tested using t-test statistic and the other, using Mann-Whitney U-test at 0.05 level of significance. The major findings from the study revealed that there is significant difference in the posttest mean scores of experimental and control groups in favour of experimental group. It also revealed significant difference in the retention ability of chemistry students taught electrolysis Concept using Computer-Assisted Instruction and those taught using lecture method in favour of experimental group. Furthermore, students exposed to computer-assisted instruction developed positive attitude towards electrolysis Concept than lecture group. The study found CAI an affective teaching method, and based on that findings emanating from this study it was recommended that Federal and State Governments should adequately trained chemistry teachers on using Computer-Assisted Instruction in teaching Chemistry.