In Italian the s is voiced between vowels. This is also the case in French and Portuguese. However, in southern Italian dialects, the intervocalic s is voiceless.
The following Italian words have an intervocalic s and are pronounced /z/ in northern and central Italy:
casa (house)
chiesa (church)
cosa (thing)
famoso (famous)
fase (phase)
mese (month)
naso (nose)
paese (country)
rosa (rose)
sposa (wife)
In southern Italy, the intervocalic s is voiceless. It is thus pronounced /s/. This is the same pronunciation that is used in Spanish.
One feature that distinguishes the Italian of northern and central Italy from southern Italy is the intervocalic s. It is voiced in the northern and central varieties, but it is not in the southern. The voiced pronunciation is considered standard.
