To clarify the species validity of the genus Spirometra, the biological characteristics of Spirometra erinacei and S. mansonoides by developmental stages were compared. Their experimental life cycles were maintained under the same laboratory conditions, and the biological characteristics were experimentally observed in vivo and in vitro conditions. Eggs of S. erinacei and S. mansonoides were $59.6pm35.6{mu}m;and;61.4pm35.8{mu}m$ in each average size. Both of them became fully matured and hatched in 8 days after incubation at $29^{circ}C$. The coracidium of S. erinacei was $43.6 imes35.8{mu}m$ in average size, and retained a oncosphere of $39.3 imes31.0{mu}m$. That of S. mansonoides was $43.0 imes36.3{mu}m$ in average size, and retained a oncosphere of $38.3 imes30.8{mu}m$. Procercoids of S. erinacei were somewhat larger than those of S. mansonoides. Both species of procercoids older than 7 days in cyclops had minute spines at the anterior end, calcium corpuscles in the parenchyme and a cercomer at the posterior end. The procercoids older than 4 days in cyclops were infective to tadpoles. The procercoids older than 8 days revealed the infectivity to mice. Plerocercoids of S. erinacei were somewhat lager than those of S. mansonoides when they were compared by age of worms in tadpoles. Both species of plerocercoids older than 5 days were infective to mice. Among 138 plerocercoids of S. erinacei recovered from the experimental mice, $55(39.9\%)$ were detected in the neck portion, $35 (25.4\%)$ in the back portion, $25(18.1\%)$ in the anterior legs, and $23 (16.7\%)$ were found in the abdomen. In case of S. mansonoides plerocercoids, $42.0\%$ were found in the neck portion, $23.8\%$ in the back portion, $14.4\%$ in the abdomen, $13.3\%$ in the anterior legs, and $6.1\%$ were found in the posterior legs. From the above results, it was confirmed that the biological characteristics of S. erinacei and S. mansonoides are almost same when their life cycles are mainteined under the same laboratory condition. Accordingly, these findings suggest that S. erinacei and S. mansonoides may be the same species.