Derivatization of neutral steroids for increasing sensitivity in liquid chromatography/negative atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) has been examined. Under APCI conditions, gas-phase electrons are provided by the corona discharge and captured by electron-affinitive compounds. In negative APCI-MS, therefore, ultrahigh sensitivity can be obtained by tagging neutral steroids, whose ionization efficiencies are low in the conventional APCI-MS, with electron-capturing moieties, such as a nitro group. We synthesized various boronic acid and hydrazine derivatives having electron-capturing moieties as derivatization reagents for 1,2-diol compounds and oxosteroids, respectively. Among reagents examined, those having the 2-nitro-4-trifluoromethylphenyl moiety were most effective in increasing sensitivity. That is, the detection responses of the derivatives with these reagents were increased by several to more than 200-fold over intact steroids, where limits of detection were some picograms. The developed derivatization procedures were applied to analyses of small amounts of steroids in human plasma and gave satisfactory results.