The sintering behavior of UO$_2$-Gd$_2$O$_3$fuel pellets under H$_2$gas has been investigated using dilatometry and XRD methods. The addition of TiO$_2$or Al(OH)$_3$increased the density and grain size. A density of 95% TD and a grain size larger than 6 ${mu}{ extrm}{m}$ are achieved by the addition of 0.1 wt% TiO$_2$or Al(OH)$_3$. It was found that the densification of UO$_2$-Gd$_2$O$_3$pellets was suppressed in the temperature range of 1300 to 150$0^{circ}C$, compared to UO$_2$pellets. The formation of a (U,Gd)O$_2$solid solution is the main reason for the suppression of densification. The role of TiO$_2$in densification and grain growth is discussed on the basis of the densification cuwe and ceramography.