Abstract: Powders of Piper guineense and Spilanthes mauritiana, potential mosquito larvicides, were assessed to determine their impact on non-target aquatic macro-invertebrates and vertebrates. Field tests were conducted in Kilifi District, Kenya on field populations of damselfly nymph (Gomphilidae), dragonfly nymph (Coenagrionidae), macro-dytiscids, micro-dytiscids (Dystiscidae), notonectids (Notonectidae), freshwater shrimps (Palaemonidae), tadpoles (Ranidae) and tilapia fish (Cichlidae). Artifical habitats were sampled and populations determined before and after application of the plant powder. Four doses (8.571, 5.714, 2.875 and 1.429 g L-1), were used in the trials and mortalities monitored after 24, 48 and 72 h. After 24 h, at 1.429 g L-1 of the powder from P. guineense and S. mauritiana, less than 20% mortality was obtained against gomphilids, coenagrionids, dytiscids, notonectids and palaemonids. At 48 h, powder of P. guineense gave 8.8 and 45% mortality against micro-dytiscids and tadpoles at 8.571 g L-1, respectively. After 72 h, at 2.847 g L-1, powder of S. mauritiana caused 6.9 and 35% mortality against micro-dytiscids and fish, respectively. The LD50s (24 h) for the organisms varied from 12.2 to 39.2 g L-1 and 13.6 to 41.82 g L-1 for P. guineense and S. mauritiana, respectively. Both plant powders showed slight negative effects on non-target aquatic macro-invertebrates and vertebrates.