To monitor root growth dynamics of rubber trees (RRIM 600) along a deep soil profile, a permanent access-well ~ 4.5 m deep was built and operated since the end of 2006. This facility allows the direct observation of root growth dynamics using so-called “root windows”, through which roots can be observed at regular time intervals. Using this access-well, we could estimate root length density and the decay of root tissues at various soil depths. Initial results were based on a 17-month observation. Some root incubations were also conducted for one year. Result from these experiments indicated that: A root growth peak occurred between May and June at a soil depths shallower than 150 cm, while it generally did not occur before November deeper in the soil profile; - Fine roots growing at all depths had a life expectancy of months rather than weeks and a large proportion survived for 12 to 17 months without showing any clear sign of senescence; - Fine root length density decreased by more than one order of magnitude from 5 to 50 cm while fine root biomass found below 100 cm still accounted for more than a third of the overall fine root biomass of the studied rubber trees; - The decay rate of dead root material at a soil depth of 400 cm was slow, with a half-life on the order of 21 months. Together with long fine roots' survival, this indicates that the residence time of carbon originating from fine rubber tree roots spans several years.