Abstract: The karyotype and chromosome number of Acacia mangium, were analysed on meristematic cell of root tips The result showed that the chromosome number in each somatic cell was 2 n=26 The 9 pairs of chromosomes (No 2, 4, 6, 8~13)were metacentric, and the 4 pairs of chromosomes (No 1, 3, 5, 7)were submetac-entric The first of pairs (No 1)was SAT-chromosome According to the classification made by L C Saylor, the karyotype formula is K(2 n)=26=18 m8 4sm(2 sat) According to the ratio of chromosome length (largest/smallest) and the proportion of chromosomes with arm ratio<2 in the comp/ement of the karyotype of Acacia mangium belongs to Stebbins "1 B" karyotype symmetry.