Field experiments were conducted in central Kenya, to study the effect of ammonium sulphate fertiliser ((NH(4))(2)SO(4)) on mosquito larval populations in rice fields. The experiments used a complete randomised block design having four blocks with two experimental ponds per block, and the fertiliser and control treatments allocated randomly among the ponds. Student's two-sample unpaired t-test was used to test for the significance of differences between the relative counts of larvae in fertiliser and control treatments. The results showed a significant overall increase in the larval populations of An. arabiensis (P<0.01) and culicine mosquitoes (P<0.05), after ponds were treated with the fertiliser. Significantly more fourth instar larvae of An. arabiensis were collected in fertiliser than control plots (P<0.001). An. arabiensis data indicated that the first fertiliser application had the most impact, compared to the second and third applications. This was evident in a significant peak of combined first and second instar An. arabiensis larvae observed 5 days after the first fertiliser application (P<0.05). The studies suggest that ammonium sulphate fertiliser reduces turbidity of water in rice fields, thereby making them visually more attractive for egg-laying by An. arabiensis and culicine mosquitoes.