Abstract <p>A method of solid-phase extraction (SPE) using carbon fiber modified with ionic liquid as adsorbent coupled with liquid chromatography-mass spectrometry (LC-MS) was developed for the determination of phytohormones. Carbon fiber was modified with amine-functionalized ionic liquid, namely 1-(3-aminopropyl)-3-methylimidazolium bromide, to prepare CF-IL through covalent functionalization. As SPE adsorbent, it was used for the determination of phytohormones during the development of cucumber fruit (<i>Cucumis sativus</i> L.) with liquid chromatography-mass spectrometry. Under the optimized extraction and elution conditions, the limits of detection of the proposed method were found to be in the range of 2.35–285 pg/mL. All the relative recoveries were in the range of 88.9 to 114.0% with RSD ≤ 9.75% (<i>n</i> = 3). It was found that levels of phytohormones were significantly changed during different developmental stages in cucumbers. Basing on obtained temporal distribution, the change characteristics of phytohormones level in cucumbers and their roles were studied.</p>