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LS I +61$^\circ$303 is a rare representative of the gamma-ray binaries with acompact object known to be a pulsar. We report on the periodicity and spectralanalysis of this source performed with more than 14 years of Fermi/LAT data.The periodicity of LS I +61$^\circ$303 is strongly energy dependent. Twoperiods $P_1 = 26.932\pm 0.004 (stat)\pm 0.008 (syst)$ and $P_2 = 26.485 \pm0.004 (stat)\pm 0.007 (syst)$ are detected only at $E>1$ GeV and at $E<0.3$ GeVcorrespondingly. Within $1\sigma$ (stat+syst) the periods are consistent withorbital ($P_2$) and beat orbital/superorbital ($P_1$) periods. We present theorbital light curves of the system in several energy bands and the results ofthe spectral analysis. We discuss the possible origin of the change in thevariability pattern between 0.1 and 1 GeV energy.

Energy-dependent periodicities of LS I +61$^\circ$ 303 in the GeV band