Karst ecosystem has been shown to be extremely vulnerable under severe water and soil erosion due to improper land uses and human activities. The karst area of Southwestern China covers a land of 550000 km² but 105000 km² of that is suffering from serious rocky desertification. Recently, national and provincial afforestation programs have been developed to protect and/or restore the degraded karst lands. Litter decomposition is the major pathway to provide organic and inorganic elements for the nutrient cycling processes and control nutrient return to the forest ecosystem. So, leaf litter decomposition and nutrient release characteristics play an important and leading role in the forest ecosystem restoration and reconstruction in the fragile karst region. In view of litter fall as the important component of forest ecosystem and the shortage study about karst area in southwest China, confronting the restoration programs. Litter bag decomposition experiments were set up at six sites to compare the litter decomposition differentiation under different karst forest ecosystems from Dec. 2008 until Nov. 2009. In this study, three typical primary forest communities (Dye-tree (Platycarya longipes Wu), Eurycorymbus (Eurycorymbus cavaleriei Hand., Wing-hackberry (Pteroceltis tatarinowii Maxim)) and three typical secondary forest ones (Round-leaved Tallow-tree (Sapium rotundifolium Hemsl), Chinese Alangium (Alangium chinense (Lour.)Harms), Negundo Chaste-tree (Vitex negundo Linn)) were chosen to elucidate the decomposition characteristics of leaf litter, release pattern of nutrient elements over the course of leaf litter decomposition, decomposition rate and related impact factors in Karst areas of northwest Guangxi of China. The result showed that the decay rates of leaf litter at primary forests were slightly faster than that of secondary forest. Release rates of carbon (C), nitrogen (N) and Potassium (K) were generally higher within initial 180 days and then tended to become stable. The content of total phosphorus (TP) in leaf litter in secondary forest communities displayed a status of net accumulation at the initial stage of decomposition, and subsequently turned to be replaced by a net release. However, the TP content of leaf litter in primary forest communities was remained in net accumulation status till 360 days after litter presence. Correlation analysis showed that decomposition rate of leaf litter was negatively correlated with total initial N content, lignin content and lignin to nitrogen ratio in leaf litter, whereas was positively correlated with leaf C/N ratio. Comprehensive and comparative analysis suggested that leaf litter decomposition rate and nutrient element release rate within the round-leaved tallow tree (Sapium rotundifolium Hemsl) community were totally greater in secondary forests than those of primary forest communities. With regard to species choices for the re-establishment of nutrient cycling in disturbed forest ecosystems, species with high nutrient recycling capacity (e.g. species with fast litter decomposition rate) may be favored. In this study, it can be argued that the tallow tree could act as a potential constructive and dominant species in the restoration of degraded Karst land and vegetation. So our study results can provide some support and refer for national and provincial afforestation programs in Karst areas of northwest Guangxi of China.