The authors previously reported that an extract from Zingiber officinale, traditionally eaten along with raw fish and used in traditional Chinese medicine, effectively destroyed Anisakis larvae in vitro. In this study, we analyzed the effective components of ginger rhizomes. Methanol extracts were fractionated after first being treated with HCl at pH 3, then with NaHCO3 at pH 10, and, finally, with NaOH at pH 13 (fraction 1). In general, this fraction is rich in neutral substances. [6]-Shogaol and [6]-gingerol, known neutral components of ginger rhizomes, were detected using gas chromatography and were found to be the most prevalent components in the fraction, occurring in quantities that resulted in a dose-dependent killing efficacy. Authentic [6]-shogaol and [6]-gingerol could kill Anisakis larvae at a minimal effective dose of 62.5 and 250 micrograms/ml, respectively. However, the concentration of [6]-gingerol in fraction 1 was greater than 20 times that of [6]-shogaol, making the former the most active component in the fraction. Furthermore, synergistic effects between [6]-gingerol and a small amount of [6]-shogaol were observed. Pyrantel pamoate, an available antinematodal drug, had no lethal effect, even at a concentration of 1 mg/ml. In saline solution containing [6]-shogaol (62.5 micrograms/ml), greater than 90% of larvae lost spontaneous movement within 4 h and were destroyed completely within 16 h. Microscopical examinations showed destruction of the digestive tract and disturbances of culticulae.