Solid nanocatalyst aluminum dodecatungstophosphate (Al0.9H0.3PW12O40, abbreviated as AlPW) with nanotube structure was synthesized through a natural cellulose fiber template. The AlPW nanotubes, which are highly water-tolerant and acid-tolerant, can be described as green double acids, as they combine both Brønsted and Lewis acid sites. They have been applied as an efficient nanoheterogeneous catalyst for the preparation of biodiesel from waste cooking oil containing 26.89 wt% high free fatty acids (FFAs) and 1% moisture via esterification of FFAs and transesterification of triglycerides in one pot under mild conditions.