We prepared functionalized magnetic nanoparticles (d = 3.5 nm) to serve as a laser desorption/ionization material for mass spectrometry. The obtained nanoparticles consisteds of a macaulayite core conjugated with hydroxyl and amino groups, and showed superparamagnetism at room temperature. The nanoparticles by themselves could ionize the sample peptide, drug and proteins (approx. 5000 Da) without causing background peaks. In the detection of biomolecules by mass spectrometry, the analytes are generally extracted from biological samples, and undergo futher purification and desaltation. However, these processing steps cause analyte loss. In the present study, we tried to detecting biomolecules in cultured cells without extraction or desaltation, but by using nanoparticles and a permanent magnet. The nanoparticles were introduced into living cells cultured on indium tin oxide-coated glass slides and accumulated on the surface of the cultured cells using an external magnetic field. The direct mass spectrometry of the cultured cells showed that we successfuly profiled the phospholipids of the cells. Our new nanoparticle-assisted laser desorption/ionization mass spectrometry technique is a quick and convenient way to profile biomolecules in cultured cells.