Provided is an apparatus and method for obtaining a vulnerable transaction sequence. A vulnerable transaction sequence obtaining apparatus may include a storage configured to transitorily or non-transitorily store at least one program; and a processor configured to receive the at least one program, to select a vulnerable transaction sequence candidate in the at least one program using a cost function, to obtain a verification condition by performing symbolic execution over the transaction sequence candidate, and to check whether the verification condition is satisfiable when the vulnerable transaction sequence is unfound as a verification result about the verification condition, and to determine the vulnerable transaction sequence candidate as the vulnerable transaction sequence when the verification condition is satisfiable.