Abstract: From early July to early November 2009, the effective leaf area index (LAI_e) of secondary Betula platyphylla forest, spruce-fir valley forest, and mixed broadleaved-Korean pine forest in Xiaoxing’an Mountains were measured with Winscanopy2006 Plant Canopy Analyzer, and the LAI_e measured in early November and calibrated with the woodytototal ratio as well as the clumping index (for clumping beyond the shoots) and the needletoshoot area ratio (for clumping within the shoots) was derived as the true leaf area index (LAI_t). In combining with litterfall method, the LAI_t and its seasonal dynamics of the three forest types were estimated. The LAI_e of the secondary B. platyphylla forest reached its peak in July, with a value of 2.21, and that of the spruce-fir valley forest and mixed broadleaved-Korean pine forest peaked in August, with the values of 2.57 and 2.68, respectively. All the three forest types had the highest LAI_t in July, with the values of 3.44, 3.86, and 6.93 for the secondary B. platyphylla forest, sprucefir valley forest, and mixed broadleavedKorean pine forest, respectively. In comparison with the method proposed in thisstudy, the peak time LAI_e of the secondary B. platyphylla forest, spruce-fir valley forest, and mixed broadleaved-Korean pine forest obtained by the optical instrument method was underestimated by 33.1%, 32.9% and 66.0%, respectively, and the LAI_e of the three forest types in the entire study period was underestimated averagely by -13.2%, 22.8%, and 56.5%, correspondingly.