Tetraploid black locust (Robinia pseudoacacia) is a woody plant with larger leaves and richer nutritional content than normal diploid black locust, with greater biomass and wider adaptability than herbaceous plant forage. However, currently no stockbreeders have adopted it as a major forage in China and other countries for a lack of information on the evaluation of nutritional ingredients of leaves and stems of young tetraploid black locust (YTBL) by in situ digesting tests. The objectives of this study were: 1) to assess the nutritive value of YTBL that bourgeoned from root stumps in the spring by determining the ruminal in situ disappearance kinetics of dry matter (DM), organic matter (OM), crude protein (CP), ether extract (EE), neutral detergent fiber (NDF) and acid detergent fiber (ADF) from leaves, stems and a mixture of both leaves and stems (MLS) of YTBL; 2) to compare these kinetic estimates with those of Leymus chinensis, a widely used ruminant forage in China. All samples were evaluated in situ by using five ruminally cannulated crossbred steers (550±22.7 kg BW). The results of 48 hours, the representative incubation period, indicate that in situ disappearance rates of DM and OM in YTBL leaves, stems and MLS are on average about 40% and can attain the level of digestibility of L. chinensis. In situ disappearance rates of leaves, stems and MLS of YTBL for CP and EE were 41% and 58% respectively, rates higher than those of L. chinensis. But the disappearance rates of NDF and ADF were, on average, respectively 30.62% and 24.89% and lower than those of L. chinensis. By analyzing synthetically all of our results it could be inferred that MLS of YTBL offers effective ruminal degradability of DM, NDF, ADF, CP, EE and OM, similar to the nutrients of L. chinensis. This supports our contention that the YTBL leaves, stems and MLS are suitable feed for those ruminants requiring high levels of nutrients, such as dairy cows and Boer goats, instead of plant forage, which is decidedly lacking in some parts of the world. Tetraploid black locust (Robinia pseudoacacia) is a woody plant with larger leaves and richer nutritional content than normal diploid black locust, with greater biomass and wider adaptability than herbaceous plant forage. However, currently no stockbreeders have adopted it as a major forage in China and other countries for a lack of information on the evaluation of nutritional ingredients of leaves and stems of young tetraploid black locust (YTBL) by in situ digesting tests. The objectives of this study were: 1) to assess the nutritive value of YTBL that bourgeoned from root stumps in the spring by determining the ruminal in situ disappearance kinetics of dry matter (DM), organic matter (OM), crude protein (CP), ether extract (EE) ) from leaves, stems and a mixture of both leaves and stems (MLS) of YTBL; 2) to compare these kinetic estimates with those of Leymus chinensis, a widely used ruminant forage in China. All samples we re results in situ by using five ruminally cannulated crossbred steers (550 ± 22.7 kg BW). The results of 48 hours, the representative incubation period, indicate that in situ disappearance rates of DM and OM in YTBL leaves, stems and MLS are on average about 40% and can attain the level of digestibility of L. chinensis. In situ disappearance rates of leaves, stems and MLS of YTBL for CP and EE were 41% and 58% respectively, rates higher than those of L. chinensis. But the By analyzing synthetically all of our results it could be inferred that MLS of YTBL offers effective ruminal degradability of DM, NDF, ADF, CP, EE and OM, similar to the nutrients of L. chinensis. This supports our contention that the YTBL leaves, stems and MLS are suitable feeds for those ruminants requiring high levels of nutrients, such as dairy cows and Boer goats, instead of plant forage, whi ch is decidedly lacking in some parts of the world