Hi aspirant,

According to the UPSC eligibility criteria,

• the candidate must be between 21 to 32 years of age.
• the candidate should hold an undergraduate degree from a recognized university. The minimum qualification must be an under graduate degree
• The UG degree could be in any field.
• For UG, you need 10 +2 qualifications

As it requires 10 + 2 higher secondary education, it is not possible for diploma holders to appear for UPSC

hope that helps.