Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae) is an important parasitoid of the oak longhorn beetle Massicus raddei (Blessig) (Coleoptera: Cerambycidae) in China. It had a long developmental period needing three years to finish a generation and its generation showed uniformity. The biological character generally was unfavored for its insect natural enemies to maintain relative stable high populations. In order to understand whether the population of the parasitoid D. helophoroides could keep its high level in forests of oak trees (Quercus liaotungenesis Koidz and Q. mongolica Fischer) or not after its releasing in forests, we investigated its potential alternative hosts in northeastern China oak forests. It was found that there were eight species of longhorn beetle species living in the east-Liaoning oak forests besides M. raddei attacking the oak trees. The numbers of four species of the longhorn beetles were predominant in oak forests, i.e. M. raddei, Moechotypa diphysis (Pascoe), Masosa myops Dalman, Stenygrinum quadrinotatum Bates. However, the vertical distributions of M. raddei, M. diphysis and M. myops on the oak trunk appeared as overlapping with the parasitoid D. helophoroides. The inoculating tests indoor indicated that the relative high parasitism rates occured in both hosts of M. myops and M. diphysis, in the former with parasitism rate 26.67% on the last instar larval stage and 43.33% on the pupal stage, and in the latter with 20.00% on last instar larval stage and 6.67% on the pupal stage. The biological observations of M. myops and M. diphysis in forests indicated that the mature larvae of the two cerambycid species existed always in a year during the unfavorable parasitism periods of D. helophoroides on M. raddei, i.e. egg and young larval stages of M. raddei (prior 3rd instar), for the parasitoid to parasitize and to maintain its high population, as well as that the two cerambycid species were the principal alternative hosts of D. helophoroides in north eastern China oak forests. The results of the present study showed evidence of that the biological control program to apply the parasitoid D. helophoroides could reach effective and sustainable control efficiency for the severe damaged wood borer M. raddei after the parasitoid was released. By parasitizing mature larvae of M. diphysis, M. myops and other six species of cerembycids attacking oaks as alternative hosts D. helophoroides could keep its relative high population, and when the proper larval stage of M. raddei (i.e. over third instar larval stage and pupal stage) for its parasitizing occurred, it then could move to the main host, M. raddei, for parasitizing. Thus, the parasitoid has a high potential as an excellent natural enemy to be used in biocontrol program to make the cerambycid under control.