depends a bit on the options of your videocard offers
there are many threads about it and everybody seems to experience different results. (or at least there are 2 groups)

Maybe search this forum a bit. We recently had a discussion in DOSBox General on the subject.

TeraNova wrote:

I'm thinking of buying a widescreen monitor soon, so I just want to know if the games on DOSBox will distorted/stretched or not?

Thanks,

they surely won't have to be distorted 😎

you will tweak either your output/resolution settings in dosbox config file, or your graphics card driver stretching options in the driver panel.

As Qbix wrote there are many threads to browse here about it 😀