To become CBI officer you need to qualify the Combined Graduate Level Examination which is conducted by the Staff Selection Commission. Following are the details of this exam:

Nationality / Citizenship:
Citizen of India or
Subject of Nepal or
Subject of Bhutan or
Tibetan Refugee who came over to India before 1st January 1962 with the intention of permanently settling in India

Eligibility:
The applicant should hold graduation or any bachelor's degree from a recognized university with minimum 50% marks.

Age limit:
The age limits are 20 years to 27 years,
3 years age relaxation for OBC candidates,
5 years age relaxation for SC/ST candidates.

The written test will cover following topics:
English Comprehension
Numerical Aptitude
General Awareness
General Intelligence and reasoning ability

Exam pattern