Can I use my passport number as my identification number in my Will?

If you have a Singapore NRIC/FIN, you should use it.

However, if you are a foreigner and do not have either, your passport number can be used to "legally identify" you. Your Will will remain legally valid even if your passport number changes subsequently.

Regardless, if you prefer to, you can also key in your other identification numbers following this article here.

In fact, for foreigners purchasing private property in Singapore, registering their marriage in Singapore or if they are a donee to a donor who has done up their Lasting Power of Attorney, they can use their passport number as an identifying detail as well!