A method of verifying data in a memory device having a page buffer for performing a program operation, a verifying operation and a read operation, includes: storing data to be programmed in a multi level cell of a first latching circuit in the page buffer; storing reference data set for the verifying operation in a second latching circuit; programming the data stored in the first latching circuit to the multi level cell; and verifying the programming of the data through a first node or a second node in the second latching circuit in accordance with a verifying voltage.