The eligibility criteria for OBC candidates in the UPSC Civil Services Exam include several key points. First, candidates must belong to a community recognized as OBC by the Central Government. Second, they must meet the age limit prescribed by the UPSC, which is generally 21 to 32 years, with relaxations applicable for OBC candidates. Additionally, candidates should possess the requisite educational qualifications, such as a Bachelor's degree from a recognized institution. It's crucial for candidates to have a valid OBC certificate to avail of the reservation benefits during the examination process.