Bamboos tend to become abundant associated with human activities and possibly affect ecosystem dynamics including vegetation water cycles. We examined the effects of thinning on canopy transpiration (Ec) for a dense, unmanaged (i.e. unthinned) Moso bamboo stand based on sap flow measurements. We unselectively thinned 45% of the culms during summer in a study plot (i.e. the first thinning). During the next spring, many new culms were generated in the plot and a comparable number of culms were thinned (i.e. the second thinning). After the first thinning, mean stand sap flux (Js) increased immediately by approximately 60% at a given potential evaporation (Ep); therefore, the Ec of the thinned stand reached 90% that of the pre-thinning condition. During the next year, after the second thinning, the Js of the current year culms was generally more than twice that of the pre-thinning stand at a given Ep, whereas the Js of the older culms decreased again to the level of the pre-thinning condition. The overall Ec was 78% that of the pre-thinning condition. Our results suggest that moderate thinning of dense Moso bamboo stands may not have major effects on Ec; thus, intensive thinning is required when the aim is to control water loss from bamboo stands. The relative insensitivity of water use in bamboo stands after thinning resulted from dynamic changes in water use in the individual culms. These processes might be related to the clonal nature of bamboo where culms are structurally and physiologically interconnected.