Fin efficiency of serrated fins was analyzed, and an analytical solution, theoretical fin efficiency, was derived as a function of modified Bessel functions. Furthermore, an approximate equation was given for the theoretical fin efficiency, which enables the calculation with a pocket calculator with an accuracy of ±1.5 %. In the analysis of the theoretical fin efficiency, however, two assumptions were employed, i. e.，uniform heat transfer coefficient over the fin surface and thermal insulation at the end surface of segmented sections. To compensate these assumptions, a correction factor was introduced and determined experimentally. Using this correction factor together with the theoretical fin efficiency, the actual fin efficiency can be estimated for serrated fins of various fin geometries, including plain fins.