The absolute value of the efficiency of electron injection from an excited coumarin dye (NKX-2311) into a nanocrystalline ZnO film was estimated as 0.8 +/- 0.1 through transient absorption measurements. This value was obtained by using the molar absorption coefficient of the oxidized form of NKX-2311 determined in solution. Using this value and the previously obtained relative injection efficiency, we estimated the molar absorption coefficients of the oxidized form of N3 dye (cis-bis(4,4'-dicarboxy-2,2'-bipyridine)dithiocyanato ruthenium(II); Ru(dcbpy)(2)(NCS)(2)) and the conducting electrons in the ZnO film.