<b><i>Purpose:</i></b> We report 2 patients with dry eye disease followed up using the expression levels of ocular surface mucin. <b><i>Case Reports:</i></b> Patient 1: a 57-year-old woman with Sjögren's syndrome-associated dry eyes experienced severe dryness and foreign body sensation in both her eyes, and instilled sodium hyaluronate ophthalmic solution 0.3% about 10-15 times daily. We measured the expression levels of MUC5AC mRNA <i>(MUC5AC)</i> and MUC16 mRNA <i>(MUC16)</i> by using real-time reversed transcription polymerase chain reaction for the specimens of modified impression cytology. Expression levels of <i>MUC5AC</i> and <i>MUC16</i> on her ocular surface were very low. Subjective symptoms and expression levels of ocular surface mucin improved after combined treatment of rebamipide (4 times daily) and fluorometholone (once daily) ophthalmic suspension. Patient 2: a 62-year-old man with chronic graft-versus-host disease-associated dry eye experienced severe foreign body sensation and developed superficial punctate keratopathy with mucous thread and filamentary keratitis. Expression level of <i>MUC5AC</i> was very high at baseline. Subjective symptoms and expression levels of ocular surface mucin improved by combined treatment of rebamipide (4 times daily) and fluorometholone (once daily) ophthalmic suspension. <b><i>Conclusion:</i></b> Clinical test for <i>MUC</i> gene expression on the ocular surface was found to be useful in the follow-up of dry eye treatment.