In this work, low-Density Polyethylene (LDPE) films incorporated with 2-methylthio-4-ethylamino-6-tert.butylamino-triazin-1,3,5, or Terbutryn (TT) was used as anti-algal agent, at different concentrations were evaluated for anti-algal performances. Clear zone test and chlorophyll a measurement method were used for anti-algal evaluations against Chlorella vulgaris (TISTR 8580) and Phormidium angustissimum (TISTR 8979) as testing algae. Mechanical properties and surface color changes of LDPE were also observed for the effect of algaecide addition. It was found that addition of TT in the LDPE specimen did not significantly alter the tensile strength, tensile elongation and toughness properties of materials. For anti-algal test, it should be noted that the greater clear zone area (clear zone test) or smaller chlorophyll a content (chlorophyll a measurement method) the better anti-algal activities. It was found that the clear zone of the TT filled LDPE sample was observed with C. vulgaris but was not seen with P. angustissimum. When the TT concentration in LDPE was greater than 600 ppm, the C. vulgaris did not grow.