The main differences between new and malloc() are:

1. new is type-safe and automatically calculates the required memory size based on the object type, while malloc() is not type-safe and requires manual size specification in bytes.
2. new calls the constructor of the object being created, ensuring proper initialization, whereas malloc() does not invoke any constructor.
3. new returns a pointer to the type being allocated, while malloc() returns a void* pointer that requires a typecast.
4. new throws a std::bad_alloc exception if memory allocation fails, while malloc() returns a NULL pointer for error checking.
5. new is preferred in modern C++ programming, but malloc() may be necessary when working with legacy code or interfacing with C libraries.