In the present study a laboratory decay assessment was carried out on 17 timbers and the data obtained were compared with field data for evaluation. A modified version of the ASTM D 2017 American Standard Testing procedure for decay was used to assess 17 Malaysian timbers for their resistance to decay by the fungus Coriolus versicolor. The weight loss of each timbers obtained from the standard test procedure was compared to those parameters to establish a regression equation(In addition to various parameters of the timber namely density, water absorption, extractives, pH, lignin content, proportion of vessel elements and ratio of fibres elements were determined for each timber). Factors that have low correlation between each other but have high correlation to weight loss were chosen to derive a regression equation for estimating durability. The above 17 timbers were also tested for natural durability in field trials located in different parts of the world. In order to compare the lab data to natural durability a criteria for classification of timber was made- timber with less than 3;wt. loss classified as very durable, 10-30;wt. loss as moderately durable, greater than 305 wt. loss as non durable. The data from the field trials also support this classification. Hence the regression equation can be used to estimate the natural durability of a timber whose resistance to decay is yet unknown.