One of quality education predictors is teacher effectiveness. This occurs when teachers utilize relevant instructional resources. Studies have established that relevance of instructional resources makes environment conducive for learning and therefore contributes immensely to the effectiveness of the teachers in the learning process. In Nyakach Sub-County, concerns have been raised on the effectiveness of teachers with regard to the relevance of instructional resources in use during the learning process. This article therefore, purposed to establish the relationship between the relevance of instructional resources on teacher effectiveness during the teaching of Literature lessons. The study is conceptualized on the effect of the interaction between Independent Variable (Instructional resources-relevance of instructional resources) and Dependent Variable (Teacher effectiveness). Correlational and descriptive survey designs were adopted; target population was 140 high school teachers teaching Literature and 52 High school principals while the sample was 42 teachers of Literature and 17 principals. Systematic random sampling and purposive sampling techniques was used to select Teachers and principals. Data collection instruments were Classroom Observation Guide (COG), Teacher Questionnaire (TQ) and Head of Institution interview schedule (HOIIS). Reliability was established by piloting 10% of the population using test-retest method. Chronbach’s alpha was used to determine instruments’ reliability with COG and TQ coefficients being 0.833 and0.797 respectively thus considered reliable. Face and content validity were ascertained by experts. Analysis was done through descriptive and inferential statistics. These were by means, standard deviation and multiple regression. Findings indicated that level of relevance towards instructional resources has significant relationship at, (r=0.215, p-value=0.0005<0.05) with regard to teacher effectiveness. The study concludes that instructional resources were irrelevant and level of relevance has statistically significant relationship with teacher effectiveness. This means that provision of instructional resources should focus more on level of relevance. These findings may be useful to principals, teachers and curriculum developers in making informed decision with regard to the provision of relevant instructional resources in secondary schools.