Agricultural advisory services play a key role in disseminating agricultural information and technology to farmers. This study aims to assess the impact of agricultural advisory on improving agricultural productivity in Benin. The study uses cross-sectional data collected from randomly selected maize and cotton farmers located in the cotton basin of northern Benin. A total of 809 cotton and maize farmers (with access to farm advisory services or not) from 81 villages in the study area were selected. To overcome selection bias and the problem of endogeneity associated with the impact assessment, regression with endogenous treatment effect model was used. Besides assessing the effect of the farm advisory on productivity, this model also has the advantage of highlighting the main factors determining farmers’ access to advisory services. The results show that access to advisory services has a positive and significant impact on farm productivity. Maize and cotton farmers with access to the advisory services have a higher yield (yield improvement of 552.3 kg/ha and 668 kg/ha for maize and cotton, respectively) compared to their counterparts without access. In addition to access to agricultural advice, education, membership of farmers’ group, use of tractor, quantity of mineral fertiliser, use of cover crops, access to credit and the number of cattle have a positive effect on productivity. On the other hand, age, household size, and use of improved varieties have the opposite effect. Furthermore, the main factors influencing farmers' access to extension services are age, gender, membership of a cooperative and distance between village and the municipal town. Strengthening the capacity of extension services is therefore essential for improving agricultural productivity. Key words: Agriculture, advisory services, maize productivity, cotton, North Benin.