Abstract: The time-temperature profiles of open or sealed tapioca starch systems with different moisture contents subjected to microwave processing were established and the multi-level structures of tapioca starch after irradiation were investigated.For both open and sealed systems, the lower the moisture content in tapioca starch,the faster the temperature rose, and isothermal transformation occurred in the starch samples.The time of isothermal transformation became longer with the rise of moisture content.Moreover, the interval lengths of isothermal transformation were also more obvious with the samples irradiated in open beakers as compared to those irradiated in sealed beakers.FTIR data suggested no new functional groups on the molecular chain of starch irradiated by microwave, only the infrared crystalline indices of the starch samples slightly decreasing.After irradiation, microscope (or polarizing microscope) data indicated that the crystal structure of the tapioca starch changed, but its morphologic structure remained unchanged.It was believed that tapioca starch food irradiated by microwave is safe for human being and other creatures.