An extracellular polysaccharide TP1A was purified from the fermented broth of Trichoderma sp. KK19L1 by combination of Q Sepharose fast flow and Sephacryl S-300 chromatography. TP1A was composed of Man, Gal, and Glc in a molar ratio of about 3.0:5.1:8.1. The molar mass of TP1A was about 40.0 kDa. Methylation and NMR analysis indicated that the probable structure of TP1A was [-> 4,6)-alpha-D-Glcp(1 -> 6)-beta-D-Galf(1 -> 6)-beta-D-Galf(1 -> 2,6)-beta-D-Galf(1 -> 2,6)-beta-D-Galf(1 -> 2,6)-beta-D-Galf(1 -> 2,6)-alpha-D-Manp(1 -> 2,6)-alpha-D-Manp(1 ->] with [alpha-D-Glcp(1 ->] and [alpha-D-Manp(1 -> 6)-alpha-D-Glcp(1 -> 6)-alpha-D-Glcp(1 ->] as branches. The antitumor study showed that TP1A was able to inhibit the cell viability of HeLa and MCF-7 cells. TP1A could arrest HeLa cells in G2/M phase and induce HeLa cell apoptosis. These findings suggest that fungal polysaccharides could be a potential source for antitumor agents.