  A theory of low-temperature phonon-drag magnetothermopower $S_{xx}^g$ is
presented in graphene in a quantizing magnetic field. $S_{xx}^g$ is found to
exhibit quantum oscillations as a function of magnetic field $B$ and electron
concentration $n_e$. Amplitude of the oscillations is found to increase
(decrease) with increasing $B$ ($n_e$). The behavior of $S_{xx}^g$ is also
investigated as a function of temperature. A large value of $S_{xx}^g $($\sim$
few hundreds of $\mu $V/K) is predicted. Numerical values of $S_{xx}^g $ are
compared with the measured magnetothermopower $S_{xx}$ and the diffusion
component $S_{xx}^d$ from the modified Girvin-Jonson theory.
