The study was carried out in Tongeren Sub- County, Bungoma county to find out the causes of declining performance in Mathematics subject in most secondary schools. Since Mathematics is a fundamental field subject it plays a pivotal role in the advancement of science and technology. Recent years have been experiencing declining performance in Mathematics the research aims in finding out the causes of declining performance. The study was guided by the following objectives; To examine the extent to which teaching methodology, poor infrastructure, students visualization of content and inadequate teaching resources influence Mathematics performance. The study targeted a population of 10 public secondary schools in the subcounty. 10 public Secondary schools have 10 principals, over 20 Mathematics teacher and 5000 students. The research used questionnaires in order to get confidential and, first-hand information. Data collected was analyzed using tables. The study found out that the declining performance in most schools was due to various causes , poor infrastructure, negative attitude and inadequate resources . Therefore, the students, parents and teachers should start working to ensure that everybody plays his role as required for them to record better results in the coming days. proper implementation of TSC policies should be done to ensure better performance in Mathematics. By understanding the root causes of declining performance, the stakeholders that is MOE can now work to develop affective solution to ensure that Mathematics continues to grow and expand.