Abstract: XRFS was applied to the determination of 12 elements in sea sediments (including S, Al, Fe, Ca, K, P, Ti, Mn, Cl, Si, Na and Mg) with preparation of sample piece by fusion with mixed flux of Li2B4O7 and LiBO2 (67+33). A portion (0.500 0 g) of sample after dried at 120 ℃ for 8 h was mixed with 5.000 g of the flux in a Pt-Au crucible, pre-oxidized at 600 ℃ for 200 s and then fused at 1 000 ℃ for 9 min. The melt in the crucible was cooled and a disc-shaped sample piece was formed which after demoulding was used for XRFS determination of the elements. Matrix effect and interferences due to overlapping of spectral lines of co-existing elements were elininated by applying the theoratical α coefficient method. Two CRM′s of sea sediments were analyzed by the proposed method, giving results of 12 components in consistency with the certified values.