We present new spectroscopic and BVRI photometric observations of the double-lined eclipsing binary AV Del ( period ¼ 3:85 days) conducted over six observing seasons. A detailed radial velocity and light-curve analysis of the optical data shows the system to be most likely semidetached, with the less massive and cooler star filling its Roche lobe. The system is probably a member of the rare class of ''cool Algol'' systems, which are distinguished from the ''classical'' Algol systems in that the mass-gaining component is also a late-type star rather than a B-or A-type star. By combining the spectroscopic and photometric analyses, we derive accurate absolute masses for the components of M 1 ¼ 1:453 AE 0:028 M and M 2 ¼ 0:705 AE 0:014 M and radii of R 1 ¼ 2:632 AE 0:030 R and R 2 ¼ 4:233 AE 0:060 R , as well as effective temperatures of 6000 AE 200 and 4275 AE 150 K for the primary and secondary, respectively. There are no obvious signs of activity (spottedness) in the optical light curve of the binary.