Provided is a method and apparatus for reserving a session resource in an IPv4/IPv6 combination network system. It allows a node to simultaneously establish an end-to-end session and a tunnel session by notifying a starting node of the tunnel session in advance about whether a last node supports RSVP while assigning IPv4 address information to an IPv6 host according to DSTM upon reserving a resource according to an RSVP mechanism in a 4over6 dual stack transition mechanism (DSTM) environment.