Compared with ordinary Pulverized Coal Combustion (PC) fly ashes, Fluidized Bed Combustion (FBC) ashes have some special properties. The effect of FBC ashes content on the strength of cement mortar was studied, and the physical properties of FBC ashes-cement mortar with 30% FBC ashes were also investigated. The results show that the flexural and compressive strength at 7 and 28 days of the mortar gradually decreases with the increase of FBC ashes content. Under the same dosage, the strength of FBC ashes-cement mortar is greater than that of PC fly ashes-cement mortar. The FBC ashes-cement system presents a normal setting time but poor soundness with more than 3.5% SO3. This work confirms that the properties of FBC ashes-cement system are superior to those of PC fly ashes-cement system when SO3 content is no more than 3.5%.