In 2011, Malaysia's Ministry of Education has implemented a new education policy called Standard Based System for Malaysian national primary schools. It is known as Primary School Curriculum Standard or Kurikulum Standard Sekolah Rendah (KSSR) which focuses on improving the learning process of the students.  However, there are many implementation concerns that need to be addressed in order to ensure the effectiveness of this current system.  Therefore, this study intends to explore teachers' challenges in the implementation of the standard-based system in Malaysian Primary schools.  A descriptive correlational research design which integrated survey questionnaires and interviews has been employed to a total of 290 teachers from national primary schools in Selangor.  The findings of the study showed that teachers were facing some key challenges such as belif, teaching and learning, motivating students, support group and pofessional development factors that hinder the process of the system in schools.  Identifying and overcoming these factors will enhance the implementation of Standard-based Assessment system in Malaysia.