In order to clarify the position of the Frasnian/Famennian (F/F) boundary in the Lower Member of the Hongguleleng Formation of northwestern Junggar Basin, Xinjiang, carbon isotope characters were comparatively studied for the carbonates from the Lower Member of this formation in the Bulongguoer section of Junggar and the interval (lower-middle Famennian of the Upper Devonian) at the Xikuangshan section of central Hunan. The age of the Lower Member of the Hongguleleng Formation is re-investigated, on the basis of its integrative biostrati-graphical evidence, carbon isotope features, and a comparison with carbon isotope data from the Xikuangshan section. The carbon isotopic trend from the Lower Member of the Hongguleleng Formation does not show any prominent positive excursion and is distinctly different from the δ¹³C oscillation pattern across the F/F boundary recorded in several typical sections around the world; the δ¹³C values at Bulongguoer vary from 0 to 1‰, which is lower in amplitude than the currently known positive shift (2‰-3‰) across the F/F boundary in the world. The Lower Member of the Hongguleleng Formation probably may not contain Frasnian deposits, or even lacks the basal part of the Famennian (Pa. triangularis conodont Zone). For the early-middle Famennian interval of the studied sections, the carbon isotope trend seems to be well comparable; and this trend can be divided into three phases: two positive-negative oscillation cycles, followed by a weak positive excursion. The characteristics of major elements indicate that the lower part of Unit 3-1 in the Bulongguoer section was affected by terrigenous supply, which is inferred to probably be related to strong regional tectonic activities.