A novel method was developed for suspension culture of anchorage-dependent animal cells using biodegradable polymer nanospheres. The addition of poly(lactic-co-glycolic acid) nanospheres (907 nm average diam.) to the culture of human embryonic kidney 293 cells in stirred suspension bioreactors promoted the aggregate formation and cell growth (4.4-fold versus 2.2-fold growth for 7 d), compared to culture without nanospheres. This method may be useful for the culture of various types of anchorage-dependent animal cells in large-scale suspension bioreactors.