Hello,

The eligibility for UPSC is to have attained 21 years and passed graduation in any discipline from a recognized university, even final year candidates too are eligible to apply fo this,

Now, coming to your question, see UPSC doesn't discriminate hence it has allowed people from every discipline to appear for this prestigious examination, if you're asking this question in reference to success ratios, then let me tell you in the past few years, specially among toppers there have been many people from engineering background, so it all boils down to preparation and strategy. Yes, UPSC is more humanities oriented, and for most of science students they have not read these subjects at 10+2 level,so for them they have to start afresh, but eventually it's your hard work, planning, strategy is what matters.