Various derivatives of aphidicolin (1) were prepared and their inhibitory effects on purified DNA polymerase α in vitro were assayed. Among these derivatives, the new 3α-, 17, 18-trihydroxyaphidicol-15-ene (24) was as inhibitory as the known 3-deoxy-and 3-oxoaphidicolins, (20) and (14). All the other derivatives with modification of any of the hydroxyl groups of 1 had no effect on the enzyme in vitro. The structure-activity relationships are discussed concerning functionalization on the aphidicolane ring.