Based on field investigations and analysis of the natural distribution of Quercus mongolica in P. R. China, eight populations of Q. mongolica (Daxinganling, Jiaying, Shuangyashan, Jiaohe, Daqinggou, Kuandian, Wulinshan and Zhanhuang) and one population of Quercus liaotungensis (Xiaolongmen as control) were selected and investigated. Material collections and measurements were made on the nine populations(thirty individual plants each population). Genetic diversities were evaluated and compared at three levels of morphology(i.e., apical bud, leaf, seed and cupule for nine populations), allozyme(nine populations) and DNAs(AFLP analysis on four populations) in order to determine core germplasm of Q. mongolica and put forward effective methods for conservation of the genetic diversity. Main results obtained are as follows:(1) Morphological diversities among/within populations were discussed by analyzing characters such as apical bud, leaf, acorn and cupule. Analysis of variance for all characteristics were significantly different among populations and among individuals within population. The mean phenotypic differentiation coefficient (VST) shows that the variation among populations(56.09%) is slightly higher than that within population. The acorn becomes larger, the shape of the acorn changes from nearly spherical to oblong, and leaf shape of the longitude and latitude, upon increasing of the lonitude and latitude. The acorn gets smaller as the altitude becomes higher. There exists correlations among the morphological characters mentioned above. According to the correlation analysis, the populations of Q. mongolica investigated may be divided into two groups and four sub-groups.(2) A gel electrophoresis method was used to study the genetic diversity of eight Quercus. mongolica populations located at Daxinanling, Jiayin, Shuangyashan, Xiaoxinganling mountain, Heilongjiang Province, Jiaohe, Jilin Province, Kuandian,Liaoning Province, Daqinggou, Inner Mongolia Autonomous Region, Wulingshan, Zanhuang , Hebei Province, and one Quercus liaotungensis (a variety of Q. mongolica) population at Donglingshan, Beijing. Twelve of 22 loci from 13 enzymes assayed were polymorphic. Quercus mongolica maintained low level of genetic variation as compared with the average Quercus species. At species level, the mean number of alleles per locus (A) was 1.905, the percentage of polymorphic loci (P) was 52.38%, and the observed heterozygosity (Ho) was 0.092. At population level, the estimates were A=1.421, P=28.976%, and Ho- 0.088. Genetic differentiation (Gst) was high among populations, Gst was 0.107, and the means of genetic distance 0.0121. The Nei's genetic identity ranged from 0.974-1.00. The gene flow was 2.0799. In contrast, the estimates for Quercus liaotungensis were almost the same ( A=1.5, P=36.36%, Ho=0.070).According to the UPGMA cluster analysis based on the genetic distance , 4 populations located in northeast and 2 populations in southwest of the geographical distribution are classified into 2 sub-groups in separate, there was no clear relationship between genetic distance and geographic distance among populations.(3) Three Q. mongolica populations located at Jiayin, Xiaoxinganling mountain, Heilongjiang Province, Daqinggouin Inner Mongolia Autonomous Region, and Wulingshan in Hebei Province, and one Q. liaotungensis (a variety of Q. mongolica) population at Donglingshan in Beijing, totally 96 individuals were selected and analyzed by amplifications using 4 pairs of AFLP primers screened, 63-113 bands produced each primer pair and 346 polymorphic locus were obtained. As for Q. mongolica, Shannon's information index (I) is 0.246 and Nei's gene diversity index (H) is 0.1453, genetic differentiation coefficient among populations (Gst) is 0.077. As for Q. liaotungensis, Shannon's information index is I = 0.220 and gene diversity index H = 0.134. Genetic identities among the four populations were high as above 0.978 ,this indicated that the low level of genetic differentiations between Q. liaotungensis and Q. mo