Nanospheres were produced by molecular assembly between tannin and gelatin because of the synergistic interaction of the hydrophobic effect and hydrogen bonding. The factors that influenced the production of nanospheres, such as sample concentration, mass ratio between tannin and gelatin, reaction temperature, pH, and reaction time, were studied. Moreover, the nanospheres were analyzed and characterized by a particle size analyzer, UV-vis spectrophotometer, and TEM. It was concluded that the critical point was important for the assembled nanospheres. The tannin/protein mass ratio should be lower than the critical point. The concentration of tannin should be confined to a relatively low level. The proper range of the reaction temperatures was usually between 10 degrees C and 50 degrees C. It was steady for nanospheres assembled when the pH value of the gelatin solution was within +/- 1 IEP of the gelatin. After the reaction had gone on for more than 48 h, the assembled nanospheres became stable. (c) 2006 Wiley Periodicals, Inc.