The 30-year-old singer, who married Canadian hockey player Mike Fisher in 2010, said she isn't ready to start a family.
"I don't feel old enough to have kids," she said. "I know I am mature. But being responsible for another human?"
Underwood also tells the mag that she's not overly sentimental about anything and that she's never been a "mushy person."
“I’m a little more selfish, a little more independent, a little closed. I do wish I were softer. I wish I were able to form relationships better. But hey, I mean…I’m not a sociopath," she said.
Brad Paisley, her Country Music Association Awards co-host, said that Underwood "could have been a general," remembering their first hosting gig together.
She was just this kid from Oklahoma, waiting to walk out in front of the world, to greet this audience that has got to be thinking we have no business being there. Me? I'm scared to death. And instead of panicking, she taps me on the shoulder and says, "Let's do this! Let's take it to them!"
Success startled Underwood, who admitted to having panic attacks at the beginning of her career.
It’s a physical reaction, feeling like the walls are closing in. The fans are great. It’s not their fault. I don’t ever want to come across as ungrateful. But on my end, it is hard for me to process. Because I am still just me.
Since winning the fourth season of "American Idol" in 2005, Underwood has garnered six Grammy Awards and 10 Academy of Country Music Awards. She became a member of the Grand Ole Opry in 2008, one of only 20 current members who are women.
Underwood's issue of Marie Claire hits stands May 21.