In the field of data analysis, including environmental data, it is important to know the shape of underlying density function. In this case, we often use histogram which provides an information about the board line of density's curve. However histogram can not be the best method when the true density function is continuous, as is often the cases. On the other hand, kernel density estimator is another popular one which gives a continuous function. In some practical cases, however, there is a case that some knowledges about the range of the data are previously given. For instance, data of percentage, such as mortality rate, only takes the values on [0,1]. This paper considers two different modifications in kernel density estimator for the data on known interval and compares them.