The eligibility criterion for appearing in the UPSC Civil Services Examination includes being a citizen of India, having a graduate degree from a recognized university, and fulfilling the age requirements. Candidates must be between 21 and 32 years old, though age relaxations are provided for certain categories, such as SC/ST and OBC candidates. Additionally, aspirants must meet certain physical and educational qualifications to qualify for the examination. It’s important to stay updated on public notifications regarding any changes in eligibility rules issued by the UPSC.