The sensitivity of deep-ocean heat uptake (DOH) below 700 m to the diapycnal and isopycnal diffusivities is studied using the MIT adjoint ocean general circulation model with idealized basins. The DOH sensitivity to the diapycnal diffusivity occurs mainly in the tropics and subtropics in both the Pacific and Atlantic. The sensitivity is positive, and its maximum is near 700 m. The sensitivity decreases towards the upper and lower ocean and towards the higher latitudes. Further analysis indicates that the positive sensitivity of DOH is dominantly associated with downward diffusive heat flux. It does not seem to be associated with the heat fluxes owing to convection, Gent-McWilliams (GM) mixing, and vertical advection. The DOH is also sensitive to the isopycnal diffusivity, although it occurs only in the Southern Ocean south of 40degS. The DOH sensitivity is negative in the South Pacific south of 40degS and in the South Atlantic south of 55degS, but is positive in the South Atlantic between 55degS and 40degS from 500 m to 3 km. The negative sensitivity of DOH is clearly associated with the isopycnal diffusivity, since the heat flux owing to the GM mixing is upward and proportional to the isopycnal diffusivity. The positive sensitivity, however, seems to be associated with the reduction of the GM mixing owing to the flattening of the slope of the isopycnal surface. Assuming a 50\% error bar of the observed diffusivities, the DOH uncertainty is estimated based on the adjoint sensitivities. It is about 0.4degK and 0.7degK, respectively, for the diapycnal and isopycnal diffusivities.