The synthesis of antibody-drug conjugates (ADCs) using the interchain cysteines of the antibody inherently gives a mixture of proteins with varying drug-to-antibody ratio. The drug distribution profiles of ADCs are routinely characterized by hydrophobic interaction chromatography (HIC). Because HIC is not in-line compatible with mass spectrometry (MS) due to the high salt levels, it is laborious to identify the constituents of HIC peaks. An MS-compatible alternative to HIC is reported here: native reversed phase liquid chromatography (nRPLC). This novel technique employs a mobile phase 50 mM ammonium acetate for high sensitivity in MS and elution with a gradient of water/isopropanol. The key to the enhancement is a bonded phase giving weaker drug-surface interactions compared to the noncovalent interactions holding the antibody-drug conjugates together. The hydrophobicity of the bonded phase is varied, and the least hydrophobic bonded phase in the series, poly(methyl methacrylate), is found to resolve the intact constituents of a model ADC (Ab095-PZ) and a commercial ADC (brentuximab vedotin) under the MS-compatible conditions. The nRPLC-MS data show that all species, ranging from drug-to-antibody ratios of 1 to 8, remained intact in the column. Another desired advantage of the nRPLC is the ability of resolving multiple positional isomers of ADC that are not well-resolved in other chromatographic modes. This supports the premise that lower hydrophobicity of the bonded phase is the key to enabling online nRPLC-MS analysis of antibody-drug conjugates.