This study investigated the effect of extensive reading on vocabulary development of senior secondary students in Bauchi state. It adopted an experimental research in which pre-test, post-test experimental design was adopted to find whether or not extensive reading can improve students? vocabulary development. The study had a sample size of ninety two (92) students selected from four senior secondary schools in the study area using purposive sampling technique. Three research questions were asked and three hypotheses generated. The hypotheses were statistically tested using mean, standard deviation and t-test statistical techniques. A pre-test in form of cloze test on registers of sports, education and politics was given to the students. After that, passages and articles from newspapers, magazines on sports, education and politics were given to the group of students to read before administering post test. After the post-test, it was found that the students had a higher achievement mean scores on registers of sports, education and politics. To prove the findings, the vocabulary gains of the low performer, mid and the high performer in the cloze test of sports education and politics were analysed before and after the treatment. This showed a significant improvement at the post test level. On the bases of these findings, the study concluded that extensive reading has a significant impact on the vocabulary development of students in senior secondary school level. It recommended that extensive reading should be embedded in senior secondary school curriculum and literature should be made compulsory at all levels of secondary schools in Bauchi state in order to promote the love of reading and vocabulary development.