The axionlike particle (ALP)-photon mixing in the magnetic field around gamma-ray sources or along the line of sight could induce oscillation between photons and ALPs, which then causes irregularities in the gamma-ray spectra. In this work we search for such spectral irregularities in the spectrum of PKS 2155 - 304 using 8.6 years of data from the Fermi Large Area Telescope (Fermi-LAT). No significant evidence for the presence of ALP-photon oscillation is obtained, and the parameter space of ALPs is constrained. The exclusion region sensitively depends on the poorly known magnetic field of the host galaxy cluster of PKS 2155 - 304. If the magnetic field is as high as similar to 10 mu G, the "holelike" parameter region allowed in Ref. [1] can be ruled out.