Soil enzymes play a key role in many soil processes that affect soil health and which may be adversely affected under a changing climate. We investigated the short- and long-term effects of bentonite amendments on soil catalase, invertase, urease, and alkaline phosphatase activity in a field experiment in a semi-arid region in northern China. Treatments included six rates of bentonite amendments (0, 6, 12, 18, 24, and 30 Mg ha^-1) applied only once in 2011. Addition of bentonite had a significant (P < 0.01) effect on the activity of each enzyme at different layers and days after millet sowing. Observed increases in catalase, invertase, urease, and alkaline phosphatase activities were up to 42%, 46%, 58%, and 50%, respectively, and they were approximately linear with increasing bentonite rate up to 24 Mg ha^-1 over the 5 yr experimental period. Averaged over 5 yr, the 24 Mg ha^-1 rate of bentonite amendment led to the largest effect on soil enzyme activity in all soil layers at five growth stages over the growing season. The observed increased enzyme activity suggests that bentonite can help maintain and improve soil health to support plant growth and contribute to sustainable agriculture production in a semi-arid environment.