The aim of this study was to validate a new 5-point Likert scale questionnaire that is being developed to assess secondary school science students' beliefs about the nature of scientific knowledge and scientific inquiry. Following a review of literature, it was found that out of the many existing instruments, most of them were open-ended and none were found to have been developed in the cultural context of Namibia. The beliefs about nature of science (BANOS) questionnaire is currently being developed to break the ground for future cross-sectional research on the nature of science and scientific inquiry in Namibia. The BANOS questionnaire taps from aspects of nature of science and scientific inquiry as a theoretical framework. The 35-item BANOS questionnaire was administered to a sample of 124 (39% male and 61% female) secondary school science teachers. The analysis of the instrument showed that the average inter-item correlation was reasonable at r = 0.40, the mean item-total correlations were acceptable at r = 0.63 and the reliability was very high at a = 0.96. Science teachers response pattern showed several variations indicating mixed beliefs about the nature of science and scientific inquiry. At non-parametric level, it was established that gender, science teaching and the type of science subject taught did not influence teachers' beliefs about nature of science and scientific inquiry. Further piloting of the questionnaire on adequate sample of student population is needed to enable more robust statistical analyses to assess the psychometric properties of the instrument.