We searched for the Φ−−(1860) pentaquark in the photoproduction process off the deuteron in the Ξ−π−-decay channel using CLAS. The invariant-mass spectrum of the Ξ−π− system does not indicate any statistically significant enhancement near the reported mass M=1.860 GeV. The statistical analysis of the sideband-subtracted mass spectrum yields a 90%-confidence-level upper limit of 0.7 nb for the photoproduction cross section of Φ−−(1860) with a consecutive decay into Ξ−π− in the photon-energy range 4.5GeV