Malenchus piauhyensis n. sp. from soil around lemon (Citrus limonia) roots cultivated in Campo Maior, State of Piaui, Brazil is described and figured. Males are unknown. It differs from Malenchus machadoi (Andrássy, 1963) Andrássy, 1968 and Malenchus acarayensis Andrássy, 1968 in having longer tail, slender body and anteriorly located vulva. In addition it can be distinguished from M. machadoi in having shorter spear (7.0:10.5-12.5 microns) and differently shaped lip region. From M. acarayensis it also differs in having longer body (0.47-0.51: 0.33-0.37 mm).