The low-temperature magnetic susceptibility, heat capacity, and electrical resistivity of uranium sesquicarbide have been determined down to 2 K by combining measurements carried out on samples of U 2 C 3 , containing UC as minority phase, and on pure UC specimens. The presence of spin fluctuations with characteristic temperature T SF = 7 K is revealed by a nonanalytic contribution to the specific heat behaving (well below T SF ) as T 3 ln(T /T SF ), and confirmed by a T 2 increase of the electrical resistivity and a 1 − κT 2 decrease of the low-temperature magnetic susceptibility. The analysis of the specific-heat data above T SF provides a Debye temperature D ≈ 256 K and a moderate high value of the Sommerfeld coefficient, γ ≈ 42 mJ mol −1 U K −2 . The zero-temperature many-body enhancement of the electron mass is found to be m * /m ≈ 2.7. Our data rule out the occurrence of magnetic ordering in U 2 C 3 . First-principles electronic structure calculations support the absence of a magnetically ordered ground state but suggest that dynamical spin fluctuations are responsible for the electron mass enhancement.