Abstract: Most of current digital watermarking algorithms for relational databases can only embed digital watermark into numeric data.They seldom deal with nonnumeric data.Therefore,research on digital watermarking algorithms that can embed watermark into non-numeric data is very important,which will expand the application of digital watermarking.The particularity of embedding digital watermark into non-numeric data is analyzed.A simple substitution algorithm is firstly proposed,which can embed digital watermark into single attribute.Then an improving approach is proposed to extend the previous algorithm to multiple attributes.On the purpose of making less change to the statistics of the data in watermarking,a statistic control algorithm is then proposed to improve the previous two algorithms.Finally,some relative experiments are designed to test the proposed algorithms.The experimental results show that the algorithms are effective and robust.