Fountain pen ink contains dyes, pigments, or nanoparticles as colorants; water and ethylene glycol or an organic solvent as the vehicle. The dyes in fountain pen ink are usually negatively charged acid dyes. In this study, various types of black fountain pen ink (5 dye‐based and 5 nanoparticle‐based) were investigated by ultraviolet–visible (UV–Vis) absorption spectroscopy, Ion Pair High Performance Liquid Chromatography Diode‐Array Detector (IP‐HPLC‐DAD), Matrix Assisted Laser Desorption/Ionization Time‐of‐Flight Mass Spectrometry (MALDI‐TOF‐MS), and Liquid Chromatography Quadrupole Time‐of‐Flight Mass Spectrometry (LC‐Q/TOF‐MS) analysis. UV–Vis spectroscopy of fountain pen ink samples showed different profiles despite their similar color. MALDI‐TOF‐MS analyses successfully differentiated 10 of the inks. Nanoparticle‐based ink, which is usually darker than dye‐based ink, showed the same UV absorption at 240 nm. The use of LC‐Q/TOF‐MS, however, allowed the 5 dye‐based fountain pen ink samples to be differentiated from one another. On the basis of the combined results of all analytical methods mentioned above, the discriminating power values were 0.71–1.00. Among them, MALDI‐TOF‐MS could successfully distinguish fountain pen ink samples with similar black colors and provide an easy analytical approach for the differentiation and identification of various types of fountain pens.