Species diversity and distribution of cladocerans in Nam Ngum River and Nam Cheng River in Vientiane Province, Lao PDR were studied. Samples were qualitatively collected using 60 μm plankton net from 7 localities. The samples were collected within dry season, 2010 and rainy season, 2011. Cladocerans photos were taken under light microscope and made drawing by CorelDRAW Graphic Sites12 for identification; and species lists were analyzed the relationship between some physical-chemical parameters of waters and species distribution by using Pearson Correlation method. Multivariate analysis was analyzed to ordinate species and locality by using PC-ORD version 5.1 with Nonmetric Multidimensional Scaling (NMS) method. A total of 39 species of cladocerans belonging to 26 genera and 7 families were identified included 12 new record species to Lao PDR. The richest family was Chydoridae (22 species); followed by Daphniidae (5 species), Sididae (4 species), Macrothricidae (3 species), Bosminidae and Moinidae (2 species) and Ilyocrytidae (1 speices). The most frequent encountered species was Bosminopsis deitersi Richard (found in 7 localities); followed by Ceriodaphnia cornuta Sars (6 localities), Ephemeroporus barroisi (Richard) and Moina micrura Kurz (5 localities), Chydorus eurynotus Sars, Ilyocryptus spinifer Herrick and Macrothrix spinosa King (4 localities).

Keywords: Cladocera, Diversity, Distribution, Nam ngum river, Lao PDR.