Many owners use a crate to assist in house-training their puppy.
Crates are excellent tools for house-training, as well as for giving your dog a safe place to relax throughout their life.
However, some puppies have accidents inside their crate -
the very problem you're trying to avoid by using the crate!
It's a common problem, and there are a few steps you can take to minimize it.
1. Time. A general rule of thumb is the number of months in age plus one equals the number of hours your puppy can "hold it" between needing to use the bathroom. So if your puppy is 3 months old, he should be able to go about four hours before needing to go outside. Make sure you're giving your puppy a chance to use the bathroom outside at least this often so he isn't forced to soil his crate because he can't hold it any longer.
2. Schedule. Keep your puppies meals on a regular schedule so you have an idea of when she will need to use the bathroom. If you keep track of when food and water goes in, you'll have a good idea of when she'll need to relieve herself outside.
3. Use a smaller crate. Your puppy's crate should be just big enough for her to turn around and lie down. She shouldn't be in her crate longer than a few hours (as a young pup) at a time so it doesn't need to be big enough to walk around. Dogs are naturally clean and do not like to soil where they sleep so you do not want the crate so large that the puppy chooses one side as the bathroom area. Use a separate play pen if you need to contain your puppy for longer periods of time.
4. Remove bedding. If you follow the above three steps and your puppy is still soiling his crate consider removing the bedding from his crate. Some pups learn that they can soil the crate and simply cover the mess with their bedding. Some puppies prefer to soil on something soft and porous like their bed. Sometimes removing the bedding, while unpleasant for a short time, teaches your pup that it's in their best interest not to soil in their crate since they will not want to lie in their mess.
5. Health Check. Before trying any of the above steps, make sure your puppy doesn't have a urinary tract infection, or any other type of illness, that could physically prevent him or her from holding their bladder an adequate period of time.