Previous studies have shown that the ethanol extract ofPlumbago zeylanica L. stems (EPZ) suppresses immediateallergic reactions. We extended these studies to examinethe effect of EPZ on delayed-type hypersensitivity reactions. Our results showed that EPZ (500 and 1000mg=kg), orally administered during either sensitizationstage or effector stage, effectively attenuated picryl chloride–induced delayed-type hypersensitivity (PC-DTH) inmice. In vitro, EPZ (100 and 200mg=ml) concentrationdependentlyinhibited Con A-induced splenocyte proliferationand interleukin-2 (IL-2) production but hadlittle effect on nitric oxide (NO) production from murineperitoneal macrophages activated with lipopolysaccharide(LPS). EPZ (500 and 1000mg=kg) also showed asignificant inhibition of ear swelling caused by xylene inmice. These results suggested that EPE alleviateddelayed-type hypersensitivity in mice, which might beattributable to inhibition of proliferation and differentiationof T lymphocytes as well as anti-inflammatoryactivities.