Alginate fiber, a kind of bio-based fiber, is a type of inherently flame retardant material. Can the addition of alginate fiber to cotton fiber improve flame retardancy of prepared cotton/alginate fabric? To solve this question, in the present work, flammability and thermal degradation properties of the cotton and cotton/alginate fabrics were studied by thermogravimetric analysis (TG), microscale combustion calorimetry (MCC), cone calorimeter (cone) and thermogravimetric analysis coupled with Fourier transform infrared analysis. Compared to cotton fabric, TG results showed that the addition of alginate fiber decreased initial degradation temperature (T initial ) and maximum-rate degradation temperatures (T max ) of cotton/alginate fabric; however, the addition of alginate fiber improved the char residual amount at higher temperature. MCC and cone results indicated that the addition of alginate fiber reduced the peak heat release rate value and total heat release, showing improvement on flame retardant properties of cotton/alginate fabric. The release amounts of inflammable gases, such as H 2 O, for cotton/alginate fabric, were almost the same as cotton fabric in the thermal degradation process; however, compared to cotton fabric, the release amounts of flammable gases, such as compounds containing -C-H groups, alcohol, compounds containing carbonyl groups and ethers, were reduced. On the basis of the results mentioned above, the flame retardant properties of cotton/alginate fabric were enhanced. The results obtained in the present study can supply a flame retardant method by the addition of inherently bio-based flame retardant alginate fiber to flame-retard cotton fabric and enlarge the applied fields of alginate fiber.