Native galactoglucomannans (GGMs), which were isolated from thermomechanical pulping waters of Norway spruce, were modified through cationization, carboxymethylation, and imination at the reducing end with a primary long-chain hydrocarbon amine. The derivatives were tested for their papermaking properties. The native GGMs increased the wet tensile strength as a result of the dispersion of fibrils in the wet fibre web. In wood-containing paper, GGMs increased the retention of fines and extractives without a decrease in paper strength. The GGMs also flocculated fillers effectively. The cationic GGMs were able to interact between fibrous fine material and fibres, as well as with fillers. Therefore, an electrostatic mechanism of action is suggested. Carboxymethylated GGMs are believed to bind to fibres and fines through divalent metal ions present in wood. For the amphiphilic amine-modified GGMs, the alkane chain attached to the reducing end appeared to play a key role. The tail was orientated towards the hydrophobic particles; the resulting paper was the most hydrophilic, since the hydrophobic particles were covered with the polysaccharide. Based on the present results, it can be concluded that galactoglucomannans can be modified to yield new and interesting functionalities to wet-end additives for papermaking and other purposes.