During the past few years the accelerated weathering in natural condition tests has been attracting the attention of several researchers. From 1996 to 1998, CaCO3-filled HDPE samples were exposed to degradation on a stationary rack (SR) in a field test and in a “Black Box” (BB), the accelerated natural one, carried out according to ASTM G 24, G 7 and D 4141, in the tropical humid climate of the Peninsula of Yucatan (Mexico), in two typical environments: marine-coastal (MC) and rural-urban (RU). The daily analysis of the Temperature/Relative Humidity (T/RH) complex and based on its Time of Wetness (TOW) values showed that there is a significant difference between both test environments. Periodically the polymeric specimens were evaluated using FTIR, DSC and solution viscometry to establish the photo degradation kinetic process. The results show that the BB accelerated test does not change but accelerates the degradation mechanism of the tested polymer in both environments. Also, this acceleration is higher for the RU than the MC environment.