Pre-mixed, ready-to-use injectable compositions possess certain advantages such as convenience and ease of use as compared to an ampule formulation, improved safety for patients due to elimination of dosage errors and solution contamination, reduction of medical waste, and ease of administration in emergency situations. Pre-mixed, ready-to-use Vancomycin injectable preparations though marketed have numbers of disadvantages which makes its handling and use difficult. The present invention therefore provides pre-mixed, ready-to-use injectable formulations of Vancomycin which eliminates disadvantages and difficulties of the marketed product and at the same time maintains desired stability for prolonged time.