The present invention provides an efficient data transmission method in BLUETOOTH broadcasting. The method of BLUETOOTH broadcasting generates a first broadcast packet and determines whether a slot is included in an access window. In a case where the slot is not included in the access window, a service interface (SI) information value is set to the assignment information of the slot. The first broadcast packet is then transmitted. A second broadcast packet is then generated and it is determined whether a slot is included in the access window. If the slot is not included in the access window, the SI information value is set to zero. The second broadcast packet is then transmitted. A slave receives the broadcast packets and obtains the SI information values. It is then determined whether the slave transmits data at the next odd numbered slot.