Is it safe to eat leftover pizza?

Yes. Family-size pizzas often aren't consumed in a single sitting. Leftovers are subject to the same rules of handling and storage as other cooked foods. Refrigerate leftover pizza and reheat  it to a temperature of 165 degrees F prior to eating it.
 
 Depending on the ingredients, some leftover pizzas will keep longer than others. Pizzas that are preservative-free generally won't keep as long. Because they are acidic, tomato-based sauces will generally keep longer than sauces made of cheese or other dairy-based products.
 
Source(s):
University of Illinois "Food Storage, Food Spoilage, and Food-borne Illness"