α,β-Unsaturated carbonyl compounds and 2-methylpyridines containing a 4-(dialkylamino)phenyl substituent can be used as fluorescent labeling reagents for the quantitative analysis of carnitine. 6-(4-Aminophenyl)-3-cyano-4-[4-(diethylamino)phenyl]-2-methylpyridine showed the best properties among the synthesized reagents.