Abstract: This study selected the sea urchin(Hemicentrotus pulcherrimus) as testing organism and investigated the inductive effects on urchins gene mutation of 120# fuel oil dispersed by dispersant. The experiments employed single strand conformation polymorphism(SSCP) to examine mutation in CyⅡa and SP-Runt gene. DNA sequencing was used to detect mutational site. The urchins were exposed to either seawater, oil or dispersed oil for 7, 14, or 21d. The results showed that no mutation was found in CyⅡa gene in oil and dispersed oil and substantial dose and time dependent changes were observed between the mutation in SP-Runt gene and the contaminant in dispersed oil. 120# fuel oil dispersed by dispersants exaggerated the probability of mutation in SP-Runt gene. The reasons included two parts: (i) the dispersants engendered fine oil droplets thus increasing the probability of contact between organisms and oil; (ii) the dispersants had solubilizing effects on petroleum hydrocarbon, especially PAHs, increasing the bioavailability of contaminant.