The effects of discovery and expository instructional methods on the attitude of students to biology was investigated. The sample consisted of 240 Form IV biology students randomly drawn from six selected secondary schools in the Oyo state of Nigeria. They were assigned into two groups—experimental and control. The experimental group was exposed to the discovery method, and the control group was taught using the expository method. The science class of Form IV in each of the six schools was selected intact for the study. A nonrandomized pretest-posttest control group design was employed. The major instrument was the 40–item Scientific Attitude Questionnaire (SAQ). It is a Likert-type questionnaire using five scales. Two hypotheses were tested. Analyses of the results showed that the experimental group evinced a significantly more favorable attitude to biology than the control group (t = 8.87, p < 0.01). It was also found that the high, average-, and low-ability groups in the experimental class evinced a more favorable attitude to biology than their counterparts in the control class. However, there was no significant difference in the attitude of male and female students exposed to the discovery and expository methods (F1,227 = 0.07, p > 0.999). The article concludes with a recommendation that science learning using the discovery method may enable the learner to evince more a favorable attitude toward problem recognition and problem solving than when learning is done by the expository method.