Kendall and Kylie Jenner love horsing around ... in music videos!

The two just posted a music video for Katy Perry's "Firework" to their joint YouTube account, and it's too cute!

They filmed it in Wyoming, and where they're staying looks beautiful! The girls and their best friends Maddy and Spencer sing along to Katy's tune as they ride horseback through the mountains during their annual family vacation.

We love how close Kendall, 15, and Kylie, 13, are -- and we love that they act their ages! The video is totally age-appropriate, and the only guys present are a few cute cowpokes who give the girls a lift.

Check out the end to see who makes a surprise cameo ...