This study investigated the factors militating against improvisation and utilization of instructional materials for effective teaching and learning of Mathematics in Cross River State Secondary Schools. Descriptive survey design was used. All teachers currently teaching Mathematics in the State formed the population for the study. This gave the population size of 1,500 Mathematics teachers in public secondary schools in Cross River State. The schools were later stratified into urban and rural areas. Out of a 1,500 Mathematics teachers, a sample of 150 representing 10% of the entire population was drawn through the Stratified Random Sampling technique. Improvised Mathematics Instructional Materials Questionnaire (IMIMQ) was developed, validated and used for collection of relevant data. The reliability coefficient of the instrument was assessed with Cronbach’s Alpha and yielded 0.80 which is an indicator of appreciable gain in reliability. Three research questions and three hypotheses were formulated to guide the investigation. Mean, standard deviation and t-statistics were used in analyzing data. The finding of the study revealed that the problems faced by Mathematics teachers during improvisation and utilization of instructional materials include financial constraints, lack of skills and strategies on improvisation and utilization, large class size, time constraint, unavailability of tools and lack of exposure on improvisation. The study also showed that these problem faced by teachers were not gender and location sensitive as there was no significant difference in the mean responses of male and female or urban and rural Mathematics teachers on improvisation and utilization of instructional materials. Recommendations were made among others that seminars and workshop on improvisation and utilization of instructional materials be organized for Mathematics teachers in Cross River State Secondary Schools by the authorities concerned.