MongoDB Documentation, Release 3.0.4 Step 3: Drop the index. Step 4: Recreate the index without the unique constraint. See also: Rebuild Indexes Process See also: To modify the index, you must drop the index first. The method returns a document with the status of the operation. Upon successful operation, the ok field in the returned document should specify a 1 . See Remove Indexes (page 524) for more information about dropping indexes. Recreate the index without the unique constraint. The method returns a document with the status of the results. Upon successful operation, the returned document should show the numIndexesAfter to be greater than numIndexesBefore by one. Index Introduction (page 481), Index Concepts (page 486). If you need to rebuild indexes for a collection you can use the db.collection.reIndex() method to rebuild all indexes on a collection in a single operation. This operation drops all indexes, including the _id index (page 487), and then rebuilds all indexes. Index Concepts (page 486) and Indexing Tutorials (page 517). The operation takes the following form: MongoDB will return the following document when the operation completes: Chapter 8. Indexes 526 { "nIndexesWas" : 2, "msg" : "indexes dropped for collection", "nIndexes" : 2, "indexes" : [ { "key" : { "_id" : 1, "tax-id" : 1 }, "ns" : "records.accounts", "name" : "_id_" } db.orders.dropIndex( { "cust_id" : 1, "ord_date" : -1, "items" : 1 } ) db.orders.createIndex( { "cust_id" : 1, "ord_date" : -1, "items" : 1 } ) db.accounts.reIndex()