The present invention relates to a method for manufacturing nanocellulose comprising the steps of: a) providing a cellulose-containing material wherein the cellulose-containing material contains less than 20 wt. % water, b) contacting the cellulose-containing material with oxalic acid dihydrate, and heating above the melting point of the oxalic acid dihydrate, to obtain cellulose oxalates, c) washing the mixture, d) preparing a suspension comprising the washed material from step c) and e) recovering nanocellulose from the suspension. The present invention relates also to a method of manufacturing nanocellulose intermediate which comprises the above described steps a)-c). The methods disclosed in the present invention are quick, simple, and direct. Pulp can be used as raw material. A considerable amount of free carboxyl groups are introduced. A high yield can be obtained. The methods are inexpensive.