Abstract: Abstract: 【Objective】Traditional statistical methods for mapping quantitative trait loci(QTLs)have been well established, especially for experimental populations generated with inbred lines. However, they cannot be directly applied in forest trees because such species have high heterozygosity and long-term generation. In this study, we applied the interval mapping method to an F₁ hybrid population of forest trees for multivariate trait data.【Methods】The statistical model incorporated various segregations of molecular markers, including QTLs, and different linkage phases between any adjacent markers. An R package called mvqtlmap was developed to implement the calculation in practice for parameter estimates of the statistical model. Based on the two parent-specific linkage maps of Populus deltoides and P. simonii, we performed QTL mapping for tree heights which were measured at six different time points from May 29 to September 24, 2014 with the developed software package. 【Results】Consequently, four QTLs affecting tree height were located on the female linkage map of P. deltoides, and six QTLs were found on the male linkage map of P. simonii. These QTLs were distributed on chromosomes 1, 5, 7, 9, 11 and 19, explaining an average of 0.8%-6.7% of the phenotypic variance. 【Conclusion】We therefore provided a useful statistical method with a computing tool for mapping QTLs with multivariate data from forest trees and demonstrated its application with a real example using poplar. The package of mvqtlmap is free download on the website of http://www.bioseqdata.com/mvqtlmap/mvqtlmap.htm.