TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The dispersion liquid of the fiber containing cellulose and/or its derivative having cellulose high-type crystal and cyclic group containing repeating unit of formula (I) is subjected to centrifugation with acceleration of 38900 G such that the viscosity in the rate of shear is 10 seconds-1 at 25 degrees C is 100 mPa.seconds. The polymeric cellulose composite is obtained by conjugating cellulose fiber planar structure component or cellulose fiber particles and polymer excluding cellulose. Alternately, the polymeric cellulose composite is formed by laminating layer of cellulose fiber planar structure component, inorganic film and polymeric planar structure component layer excluding cellulose. The cellulose fiber is subjected to disentanglement which includes chemical modification before ultrasonic irradiation. The disentanglement involves ejecting the dispersion liquid from high pressure atmosphere of 30 MPa or more and reducing the pressure.X1-X3=H, 1-20C alkyl carbonyl or 26C alkenyl carbonyl optionally substituted by allyl, alkenyl carbonyl, nicotinoyl, isonicotinoyl or furoyl.Preferred Composition: The concentration of the cellulose in the dispersion liquid of cellulose and/or its derivatives obtained in 10% of supernatant liquid after centrifugation is 50% or more. The content of fiber having diameter of 400 nm or more in the cellulose fiber planar structure component is 10-90 vol.%. The content of fiber having diameter of 400 nm or more in the cellulose fiber particles is 10 vol.% or less.    TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The fiber in the fiber composite is cellulose and fiber is chemical modified fiber. The matrix material in the fiber composite is polymeric material. Preferred Properties: The yellowness of the fiber composite is 20 or less based on JIS K7105 after heating the fiber composite in the thickness of 100 mu m at 190 degrees C for 1 hour in oxygen partial pressure of 0.006 MPa or less. The water absorption of the fiber composite is 1% or less based on JIS K7209(D method) in thickness of 100 mu m. The fiber composite has coefficient-of-linear-expansion of 1-50 ppm/K and thickness of 10 mu m to 10 cm. The haze value of the cellulose fiber planar structure component obtained from cellulose fiber dispersion liquid in 50 mu m thickness is 50 or less. The cellulose fiber planar structure component has porosity of 10% or less, thickness of 100 nm-1 cm and refractive index when oil is impregnated is 1.52 when measured under microscope. The cellulose fiber particle has particle size of 1 mu m to 1 mm and refractive index of 1.52.