My dog is almost one year old. She started having diarrhea 2 days ago, and it has mucus in it. Luckily she acts really normal and active. I took her stool sample to the vet for test today, they told me the result was negative and she had no worms. I already put her on diet today but her stool still contains a large amount of mucus. I have no idea what I should do. :( could anyone give me some advise? Thank you so much.

Have your recently changed her food? You said you put her on diet today, is this a different food than she usually eats. Did you change foods shortly before the diarrhea started?

Change in diet can cause runny stool if it's not done slowly. So can an allergic reaction.

Thank you for commenting! I only gave her diet can food today because my vet told me to, and she used to eat that kind of food, she was OK with it. I really wonder why would she have a large amount of mucus stool.

To play it safe, I would see if you can get into your vet today. It would suck to have your dog go downhill during the weekend when clinics aren't open and you have to pay extra for an emergency fee/emerg clinic.

I agree with saris, while sometimes a small amount of mucous may not cause concern, it sounds like your dog is experiencing quite a bit of it. It could be food related, Maybe you could ask the vet about feeding boiled rice and hamburger or chicken for a day or two to see if it clears up?