I have a 1999 honda accord and im am trying to find out if 20 inch rims will fit on the car???

 

That's like asking if you can wear a size 15 when your shoe size is actually a 10. Can you? Sure. Are you going to ruin your comfort/walking ability/etc during the day and look ridiculous in the process? Yep.

 

Should fit. I think you'll be asking for problems. braking, handling, etc like Aradin said will change and not for the better. Plus a camber kit and a general PITA

 

This is not really the forum for this modification. Wheel and Tire or Appearance forums may have a better answer to your query.
Most don't go beyond 18" more common is 17".
You didn't state if the car would be lowered/raised or even if it was a 2.3 or 3.0(there is a different tire size for the two).
If you can find a 20 x 7-8" wheel with an offset of 40-45mm you may be able to fit. With a 225/30R20 tire.
Most online shops will not have anything listed.
Best to find the local 'hood wheel shop and see what may fit your car.
FYI if you have a V6 5 lug you will have more options than a 4 banger 4 lug.

No idea if the wheels/tires will physically clear the fender at full lock and compression. Common issue I see with the Buick boys around here is a mangled front fender from going around a corner and hitting a dip at speed.