if i have 'ID' as Primary Key(data type=int32) at Database and 'UID' with data Type=GUID, and the mapping file is as below:
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
<class name="nhRegistration.Department, nhRegistration" table="Department">
<id name="id" column="ID" type="Int32">
<generator class="identity"></generator>
</id>
<property name="UID" column="UID" type="GUID" />
</class>
</hibernate-mapping>
Can my property declare as this,because i want to UID to auto generate it new GUID?

Yes, you can, but you will have to generate the GUID yourself, using Guid.NewGuid().

thank you....