This paper deals with the recent sissoo ( Dalbergia sissoo ) decline in the plain land (locally called as terai) of Nepal. This study has made an attempt to find the possible causal factor of this decline. The study has made some initiative in this aspect and has made a comparative study of 30 different sissoo forest (both natural and plantation) stands. The symptoms of the sissoo decline were found to be varied. But in most cases, the top dying of crown was found to be the most prevalent. The top dying starts from the top of the tree and progressively proceeds downward to the stem. The leaves become yellow. The other types of damage observed in the stands were: (1) defoliation by insect borers; (2) oozing of black or black reddish sap out of the stem; (3) stem covered with termites up to a certain height; and (4) the infection of the leaves with certain fungi. Until now, it has been assumed that only the plantation forests have been affected but this study observed the sissoo decline also in natural forest sites. We analysed various components of physical soil characteristics (water holding capacity, soil texture, soil density, porosity and colour) and we did not find any correlation between the physical soil factors and the sissoo decline. We concluded from this study that the soil is not the sole responsible factor involved in the sissoo decline. Furthermore, this paper discusses various aspects of the sissoo decline and possible causal factors concerned. Finally, future management strategies regarding the sissoo management are suggested.