Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) has been developed, optimized, and applied to investigate the dimethylsulfide (DMS) emissions from eight marine phytoplankton species, namely, Calcidiscus leptoporus, Emiliania huxleyi, Phaeodactylum tricornutum, Chaetoceros neogracilis, Dunaliella tertiolecta, Synechococcus, Prochlorococcus, and Trichodesmium. Four SPME fiber coatings (PDMS, PDMS-DVB, PDMS-CAR, and CW-DVB) were tested for linearity and limit of detection. Key parameters such as equilibrium and extraction times, desorption temperature and time, and headspace volume were optimized to make extraction as efficient as possible using the PDMS-DVB fiber coating. This fiber enabled the characterization of DMS in seawater under 0.005 nM levels and within 1 min exposure time. Among the different algae groups, the two coccolithophorids, C. leptoporus and E. huxleyi, were the strongest emitters of DMS. Within the cyanobacteria, Prochlorococcus and Trichodesmium expressed no DMS emission, whereas Synechococcus showed very low DMS emission. The DMS emission of C. leptoporus, however, was several orders of magnitude higher than all other algae, including E. huxleyi, which is known to be a prolific emitter of DMS.