This study investigated the challenges Form III English language teachers face when implementing the revised integrated English language curriculum. A mixed-method descriptive design was used in Eldoret East SubCounty in Kenya. Data was collected through questionnaires, interviews and reflective conversations. Cluster, purposive and random sampling were used to identify 50 study participants. Quantitative data were analyzed using descriptive statistics while qualitative analysis involved transcriptions of interviews and filed notes which were coded, categorized and patterns and themes identified. The study established that lack of appropriate Teacher Professional Development (TPD), content overload and complexity, non-suitable learner characteristics, inadequate directions in course books on integration and inappropriate pre-service training affected curriculum implementation efforts. The study recommends involvement of teachers in the development of curriculum innovations, organized Continuous TPD, development of materials that support teachers in their implementation and review of assessment procedures.