The subcritical water extraction (SWE) was employed to extract x-carrageenan from the red marine macroalgae Kappaphycus alvarezii. A series of extractions using different conditions were carried out with different ionic liquids (ILs) as catalyst, and 1% 1-Butyl-3-methylimidazolium acetate (BMIMAc) at 150 MPa with 1:80 gmL(-1) (solid to liquid ratio) exhibited the highest yield (78.75%). Extracted material was compared with samples obtained by aqueous SWE and the conventional method. Characterization of the extracts was performed using Fourier transform infrared spectroscopy (FT1R), thermal gravimetric analysis (TGA) and X-ray diffraction (XRD). Hence, the results showed comparability to the standard confirming the extracted material as typical crude x-carrageenan. Physical properties including gel strength and viscosity were minimal but emulsification index was relatively high for the sample obtained by SWE with IL catalyst. Antioxidant activity however was low compared to the other samples due to the low sulfate content but monosaccharide composition was close to the standard. The molecular weights of all samples were directly impacted by thermal degradation and IL dissolution which enhanced their bioavailability and functional properties. The SWE with IL catalyst is a potential technology that can be utilized for extraction of x-carrageenan for commercial use in different industrial sectors. (C) 2017 Elsevier B.V. All rights reserved.