Abstract: The characteristic of the isothermal moisture sorption of grilled Ulva pertusa was studied. In the experiment, moisture absorption curve from 5℃ to 40℃ were drawn, and then corresponding regression equation of each curve was obtained by curve fitting.Mathematical model of corresponding relation between dry-basis moisture content and water activity of grilled U.pertusa under the condition of 5℃ to 40℃ was established according to the curve regression equation. The results showed that the moisture sorption isotherm of grilled U.pertusa was inverse-S shape from 5℃ to 40℃. The curve regression equation obtained by computer has big correlation coefficient and small calculation error.