A small pupil and poor pupil dilation are well-known risk factors faced by veterinary ophthalmologists during and after cataract surgery. We here describe two cases of phacoemulsification performed using an iris expander (Visitec I-Ring Pupil Expander, Beaver-Visitec International, USA) for treating cataracts in dogs with small pupils. Using this technique, we performed cataract extraction effectively in dogs with insufficiently dilated pupils. This case report provides useful information on the use of an iris expander for phacoemulsification in eyes with a small pupil, which can be applied in veterinary settings.