Hydraulic and chemical pulse tests were performed in four shut-in chambers to obtain hydraulic and chemical parameters of the Callovo-Oxfordian shale. The osmotic tests, i.e., chemical pulses, were carried out by exchange of the formation water for a different solution either more or less concentrated. Two sets of two osmotic tests were done in March and October 2006. These osmotic tests are superimposed on a purely hydraulic response because of the drilling of the well causing a pressure drop. The pressure records (hydraulic and osmotic responses) were interpreted using a 2-D model to obtain the hydraulic and chemical parameters. The osmotic efficiency inferred for the Callovo-Oxfordian shale is on the order of 0.012 for a concentration of 0.43 mol L-1 and 0.12 for a concentration of 0.086 mol L-1. These results suggest that the Callovo-Oxfordian shale behaves as a weakly semipermeable membrane and only 0.1-0.15 MPa of the 0.2-0.5 MPa can be explained by these osmotic efficiency values.