We have analysed the first 15 months of Fermi /LAT data of the radio loud quasar 3C 273 . Intense gamma-ray activity has been detected , showing an average flux of F ( > 100 MeV ) = 1.4 \times 10 ^ { -6 } ph cm ^ { -2 } s ^ { -1 } , with a peak at F ( > 100 MeV ) = 5.6 \times 10 ^ { -6 } ph cm ^ { -2 } s ^ { -1 } detected during a flare in September 2009 . Together with the brightening of the source , a possible hardening of the gamma-ray spectrum is observed , pointing to a shift of the inverse Compton peak toward higher energies than the 1–10 MeV range in which 3C 273 inverse Compton emission is typically observed to peak . During the 15 months of observations the photon index is measured to vary between \Gamma = 2.4 and \Gamma = 3.3 , with an average value of \langle \Gamma \rangle = 2.78 \pm 0.03 . When compared to the observations at other wavelengths , the gamma-rays show the largest flux variations and we discuss the possibility that two different components are responsible for the inverse Compton hump emission below and above the MeV peak .