We will present the results of our observational studies of very low-mass young stellar 
objects (YSOs) including brown dwarfs and planetary mass objects in the nearby star-forming 
regions. 

We have performed deep near-infrared surveys that are sensitive enough to provide a census 
of the stellar population embedded in the clouds down to objects below the deuterium-burning 
limit (Oasa et al. 2006).

Based on the color-color diagrams, we discriminate YSO candidates with near-infrared 
excesses from reddened field stars. 
Combining the reddening-corrected luminosity of the YSO candidates with the theoretical 
evolutionary models, it is likely that there exists a substantial substellar population, 
including many potential isolated planetary mass objects. 
                       
In addition, the near-infrared spectroscopic observations of the relatively bright 
substellar YSO candidates have been carried out with the SUBARU telescope. 
Spectroscopy offers a means for more accurate assessment of cluster membership and more 
precise measurement of the mass. 
In order to estimate mass more precisely, we have measured the strength of water and 
constructed the reddening-independent water absorption index which is an indicator of 
temperature. 
Together the luminosity with the water index, we confirm that some YSO candidates have cool 
temperatures consistent with young brown dwarfs.