Mangrove forests are very complex coastal ecosystems containing various plant and animal communities, including forest floor fauna. The parameters of mangrove vegetation are thought to have a close relationship with the abundance of forest floor fauna. Therefore, the degradation of ecosystems and the reduction in mangrove vegetation, as is the case in the coastal areas of Java, can disrupt the balance of mangrove ecosystems and the presence of forest floor fauna. This study aimed to determine the composition of mangrove vegetation in two mangrove locations on the north coast of Java Island, i.e., Pondok Bali beach in Subang, West Java and Pulau Dua Nature Reserve in Serang, Banten; and determine the relationship of various vegetation parameters and the abundance of forest floor fauna. Vegetation and floor fauna data were obtained by using sampling plots of size 10 m x 10 m determined by purposive sampling. The vegetation parameters measured were tree density, root density, and canopy cover. The forest floor fauna in this study was limited to Molluscs and Crustaceans. The relationship between vegetation parameters and abundance of floor fauna was analyzed by Pearson correlation test and multiple linear regression using SPSS software. Results indicate that the two locations differ in vegetation and floor fauna community structure. Pondok Bali beach has a homogeneous plant composition, consisting of only two species, i.e., Avicennia marina and Rhizophora mucronata. Avicennia marina dominated at tree level (Importance Value Index 172%), while Rhizophora mucronata was dominant at the sapling and seedling levels (IVI 154% and 189%). Pulau Dua Nature Reserve in general has a more diverse species composition, characterized by five plant species, i.e., Avicennia marina, Rhizophora apiculata, Bruguiera cylindrica., Excoecaria agallocha, and Lumnitzera racemosa, however Avicennia marina dominates at all levels (IVI 180%, 88% and 103%). Pondok Bali Beach has higher abundance of floor fauna than Pulau Dua Nature Reserve, i.e., 16.7 ind/m². The floor fauna found at Pondok Bali beach consists of five species of Crustaceans and five species of Molluscs with abundance of 6.6 ind/m² and 10.1 ind/m² respectively. The abundance of floor fauna in Pulau Dua Nature Reserve is 8.6 ind/m². The floor fauna found in Pulau Dua Nature Reserve consists of two species of Crustaceans and six species of Molluscs with abundance of 0.35 ind/m² and 8.3 ind/m² respectively. Results of Pearson correlation tests suggest a very strong relationship between two vegetation parameters and abundance of floor fauna (i.e., tree density, R = 0.703 and root density, R = 0.737), while the canopy cover was not related to abundance of floor fauna (R = –0.029). Results of multiple linear regression analysis indicated that tree density and root density affected the abundance of floor fauna (R = 0.829 and R² = 0.687). The regression equation for this relationship is Y = –7,79 + 0,015  + 0,07  (with X₁ tree density; X₂ root density) which indicates that higher density of trees and roots will increase the abundance of fauna in the forest floor.