Cubic PbF2 crystals were grown by non-vacuum modified Bridgman method. Their optical transmission may easily be deteriorated by oxygen contamination during their growth process, annealing and afterwards machining, storing and carrying. It was found that the role of oxygen is to promote the transformation of beta-->alpha phase in the initial cubic structured monocrystals, which results in the formation of cryptocrystalline or microlithic texture composed of crystalline alpha-PbF2 grains. This texture is suggested to be responsible for the transmission loss of lead fluoride (PbF2) crystals. And the oxygen does not appear in the form of oxide, but in a dissociated form in PbF2 crystals. (C) 2002 Elsevier Science B.V. All rights reserved.