Higher education in Kenya has experienced tremendous growth since independence. With only one public university with an enrolment of less than 1000, the number stands at twenty two public universities with student population of over 150,000. This growth has been attributed to the introduction of module II programs and increased private and public funding for university education. However, despite the increase in enrolments, there has been no commensurate development and/or improvement of the requisite teaching staff and other teaching and learning resources. Consequently, concerns have been raised on the instructional effectiveness and the quality of education provided in public universities in Kenya. This study was conceived to establish the effect of the rapid expansion of university instructional effectiveness in Maseno University. The study was anchored on the education production function theory and adopted a descriptive survey design. The study was carried out in Maseno University. The target population was 7,175 comprising of 7,000 undergraduate students and 175 lecturers of Maseno University in the 2011/12 academic year. Simple random sampling was used to select 210 students and 96 lecturers making a sample of 306. Data were collected using a questionnaire for students and lecturers. Research instruments were validated using face and content validity while reliability was determined using test-retest technique at r= 0.7. A pilot study was conducted in one public university and the data was used to determine the reliability of research instruments. Data was analyzed descriptively using frequencies and percentages by aid of SPSS version 17 and presented in tables and graphs. The findings of the study showed that enrolments, especially under Module II, are on a steady rise. However, the study revealed that there was no commensurate development and improvement of teaching facilities to match the increased enrolment, which has compromised instructional effectiveness and quality of education provided in Maseno University.