An important issue arising from large scale data integration is how to efficiently select the top-K ranking answers from multiple sources while minimizing the transmission cost. This paper resolves this issue by proposing an efficient pruning-based approach to answer top-K join queries. The total amount of transmitted data can be greatly reduced by pruning tuples that can not produce the desired join results with a rank value greater than or equal to the rank value generated so far. Categories and Subject Descriptors H.2.4 [Database Management]: Systems ? query processing; General Terms: Algorithms, Design.