on or under ?

Definitely "under." "On" would apply if the grass had just been cut, and someone picked up a bunch of it and dropped it on your bare feet (or put it down your neck!) - A.

Avangi,

Thank you so much for answering my question.

If you may, may I ask an additional question?

If the "grass" was "sand" ( at beach) in that sentense, which is better ?

" I like the feeling of sand on my bare feet . "

Avangi,

Sorry, let me correct my second question due to typeo.

If the "grass" was "sand" ( at beach) in that sentense, which is better ?

" I like the feeling of sand on my bare feet . "
" I like the feeling of sand under my bare feet . "

"Under" would be the most common usage, especially if you are walking or running. But people who are "playing" in the sand often pour sand over their feet or bodies to experience the unusual feel. You'd need some context to make that clear. You can use other prepositions: "I don't like the feeling of sand between my toes or inside my underwear."

Avangi,

Thank you very much again for answering my question.

It is helpful information. I understand well.

Thanks a lot.