Parents risk being fined up to €500 (£425; $560) if they send their unvaccinated children to school. Children under six can be turned away.
The new law came amid a surge in measles cases – but Italian officials say vaccination rates have improved since it was introduced.
Under Italy’s so-called Lorenzin law – named after the former health minister who introduced it – children must receive a range of mandatory immunisations before attending school. They include vaccinations for chickenpox, polio, measles, mumps, and rubella.
Children up to the age of six years will be excluded from nursery and kindergarten without proof of vaccination under the new rules.