A B737-700 crew declared an emergency and returned to land after flight attendants reported a burning electrical smell in the back half of the aircraft. The smell dissipated prior to landing.

Narrative

We received two chimes from the flight attendants and we were notified about fumes described as burning electrical odor in the back half cabin (Row 15 and aft). Our position was approximately 50 miles northwest of our departure city. The First Officer and I discussed our options and I made the decision to return. We notified ATC and declared an emergency. We received clearance to start our descent and vectors back towards the departure airport. I maintained a high speed to expedite our landing. The First Officer completed and complied with the QRH for our issue. I sent an ACARS message to Dispatch notifying them about our problem; and that we were returning to land. We contacted the flight attendants a couple of times during our return flight. They reported that the fumes and odor seemed to have diminished. I made a PA to our customers informing them about the unidentified odor in the back cabin and that we would make a precautionary landing. After we landed; the fire and rescue personnel inspected the aircraft exterior and we were given the all clear to proceed to the gate. After we parked a logbook entry was made. Maintenance and Dispatch were briefed.