A method is described for automatted on-line micro-solid phase extraction using polydopamine-modified polystyrene/silica electrospun nanofibers as an adsorbent for monohydroxy metabolites of polycyclic aromatic hydrocarbons (OH-PAHs). They were then quantified by liquid chromatography-mass spectrometry. The sorbent has a network structure, high porosity, stability, hydrophilicity and good extraction capacity. Under optimal experimental conditions, the method has (a) wide linear ranges (0.03-25 ng·mL for 3-hydroxyphenanthrene and 1-hydroxypyrene; and 0.05-25 ng·mL for 2-naphthol), (b) good precision (with relative standard deviations from 2.0 to 12.4%), (c) high enrichment factors (24-112), (d) low limits of detection (2-21 pg·mL), and (e) acceptable recoveries from spiked samples (79.1 to 108%). The method was successfully applied for the analysis of trace OH-PAHs in urine. Graphical abstractSchematic illustration of online micro-solid phase extraction using polydopamine-modified polystyrene/silica electrospun nanofibers as adsorbent for the enrichment and determination of monohydroxy metabolites of polycyclic aromatic hydrocarbons (OH-PAHs) prior to LC-MS analysis.