By crocodile we are referring to only Crocodiles ( genus - Crocodylus), since Crocodilian family includes Crocodiles, Alligators and Gharials.
Some Crocodiles like Saltwater crocodile and Nile Crocodile are the largest large semi-aquatic reptiles alive today.
A fully grown 19.7 to 23 foot long, 2200 to 3500 pound fully grown Saltwater crocodile has almost no natural predator. Same for a 18 to 20 foot , 1500 to 2500 pound adult Nile Crocodile. Only predator of a large Saltwater crocodile or Nile Crocodile is another large rival crocodile. Crocodiles are feared for their massive jaws capable of huge bite force.
So what are the crocodiles’ natural enemies? -
Humans are the primary natural enemies of Crocodiles because till late 1970’s most of Crocodile population in the world was descimated by us for trophy hunting and their valuable armoured skin or hide.
If we are considering small and medium sized crocodiles. Bengal Tigers are threat for Mugger Crocodiles and medium sized Saltwater crocodiles especially in Indian subcontinent and parts of Sundarbans in Bangladesh. Mugger or Marsh Crocodiles are the most widespread of all crocodiles in India so they regularly confront Bengal Tigers. Indian rock python or Indian Tiger python too is natural enemy of Mugger Crocodile.
In some parts of Asia including India, Burmese pythons are also primary rivals of Saltwater crocodiles
Bulls sharks and Tiger sharks are also threat for medium sized Saltwater crocodiles in coastal waters.
In many parts of Northern territory of Australia, Sawfish and Bull sharks are primary rivals of Saltwater crocodiles.
Hippos and African Lions are primary enemies for Nile Crocodiles in Nile basin of Africa. Hippos are some of the few animals in African ecosystem that are capable of driving a fully grown Nile Crocodile from it's territory African Rock Pythons are also known to be rivals of Nile Crocodiles.
In Zambezi river, Bull sharks also known as Zambezi river sharks are primary rivals of Nile Crocodiles but are not match for these huge reptiles.
In Florida Everglades, American crocodiles face competition with invasive Burmese Pythons.
In parts of Amazon river basin, Amazon river systems particularly in Orinoco basin, endangered Orinoco crocodiles are rivaled by Giant Anacondas.