Poly(l-lactic acid)/hydroxyapatite (PLLA/HA) nanocomposite, which combines the properties of PLLA and HA, is suitable to construct scaffold for bone tissue engineering. Its mineralization behavior plays a key role in composite's property. In this present work, two PLLA/HA composites with porous and compact architecture were fabricated and soaked into simulated body fluid (SBF) at 37 A degrees C for in vitro mineralization, respectively. An attenuated total reflection Fourier transform infrared (ATR FTIR) mapping coupled with principal component analysis was developed to investigate the mineralization kinetics. The FTIR images with an area of 300 x 300 mu m(2) were collected every 7 days. The results suggest that the mineralization of PLLA/HA composites in SBF follows a zero-order kinetic model, no matter what the architecture is. However, it follows a second-order model when the composite is degraded in phosphate-buffered saline solution based on our previous work. The mechanisms of the in vitro mineralization kinetics in different submersion solutions are discussed. Our results alert researchers that they should choose the mineralization medium cautiously.