Abstract: Urban forest is an important part of forest resources of China, and it played an important role in economy, ecology, society and so on. A study on urban forest of Guangzhou was made in this paper. Plots were set up in the natural secondary forest, improved plantation and unimproved plantation, the stand structure characteristics and species diversity of undergrowth of the three different forest types were comparatively analyzed. The results showed that the arbor layer of the natural secondary forest in Guangzhou mainly consisted of Machilus chinensis, Diospyros morrisiana, Schima superba, Rhodoleia championii, Pinus massoniana, Itea chinensis and so on. The improved plantation was mainly composed of Pinus massoniana, Cunninghamia lanceolata and other introduced tree species. The main tree species of the unimproved plantation was Pinus elliottii. The number proportion of the trees with large DBH was higher in the naturally secondary forest while the trees with middle to small DBH accounted for large proportion in the improved plantation, whereas the DBHnumber curve of the unimproved plantation showed normal distribution with double peaks. More trees with height between 10m to 14m mainly distributed in the naturally secondary forest, the improved plantation approximately to normal distribution. The tree height structure of the unimproved plantation presented as asymmetric mountformed curve close to the average height of the majority trees. The species diversity of undergrowth in the naturally secondary forest was the highest, which was followed by that of the improved and unimproved plantation.