Induction of secreted acid phosphatase (APase) is a universal response of higher plants to phosphate (Pi) limitation. These enzymes are thought to scavenge Pi from organophosphate compounds in the rhizosphere and thus to increase Pi availability to plants when Pi is deficient. The tight association of secreted APase with the root surface may make plants more efficient in the utilization of soil Pi around root tissues, which is present in organophosphate forms. To date, however, no systematic molecular, biochemical, and functional studies have been reported for any of the Pi starvation-induced APases that are associated with the root surface after secretion. In this work, using genetic and molecular approaches, we identified Arabidopsis (Arabidopsis thaliana) Purple Acid Phosphatase10 (AtPAP10) as a Pi starvation-induced APase that is predominantly associated with the root surface. The AtPAP10 protein has phosphatase activity against a variety of substrates. Expression of AtPAP10 is specifically induced by Pi limitation at both transcriptional and posttranscriptional levels. Functional analyses of multiple atpap10 mutant alleles and overexpressing lines indicated that AtPAP10 plays an important role in plant tolerance to Pi limitation. Genetic manipulation of AtPAP10 expression may provide an effective means for engineering new crops with increased tolerance to Pi deprivation.