It has long been recognized that innovation plays a crucial role to support the economic performance of manufacturing firms. By contrast, the innovation in service is considered to be a less-studied topic and the empirical frameworks in this context are rather rare. As a way to overcome this gap, we analyze, in this paper, the impact of the innovation activities on the performance of the Tunisian service firms. We use the Heckman’s two-stage econometric model in order to identify the contribution of service innovation to enhance the firms’ performance (productivity, sales growth and employment growth). Based upon a sample of 71 Tunisian service firms, having significant value-added services, we show that innovation has a positive and significant effect on the productivity and on the employment growth. However, innovation has no effect on the sales’ growth.