Police believe a wheelie bin was set alight outside the back of the premises before 12.25am yesterday morning, causing up to $50,000 damage to the building.
A police spokeswoman said the fire was deemed suspicious and the Arson Squad was investigating.
West Perth resident Mrs Davies said police called her at 12.30am.
�When they told me it was $600,000 I visualised most of the shop was gone but as long as my bride�s dresses are safe, that�s all I thought about,� she said.
�It�s dreadful; I would have been a mess if we�d lost customers� dresses.�
Hob Nob, which has been at Beaufort Street for nine years, did not have electricity by mid morning yesterday as a result of the damage.
Mrs Davies said she lost 10 new dresses worth $10,000 in total.
�I�m so lucky we�re still able to open for business,� she said.