Using the 1994–2002 continuous data of CO 2 mixing ratio, CO 2 flux and meteorological parameters observed at the Takayama site located in a cool-temperate deciduous forest in central Japan, various statistical analyses are performed to examine inter-annual variations of annual mean height-dependent vertical CO 2 mixing ratio differences; these are then compared to annually integrated carbon budget components estimated from the flux measurement. The mixing ratio measurements are made at 27 and 18m (located above the canopy), and 8.8 and 5.8m (located inside the canopy) on a tower situated at the site. Relative to 27m, the annual mean mixing ratios in the lower layers show a significant positive correlation (>90 or >95% confidence level) with the annually integrated soil respiration, while a significant negative correlation (>95% confidence level) between the 18- and 27-m mixing ratio difference for the daytime data and the annually integrated gross primary production is obtained. Significant long-term trends (>95% confidence level) of the annual mean vertical mixing ratio differences are found, with an increasing trend for the daytime and nighttime data at the lower levels inside the canopy and a decreasing trend for the daytime data near the canopy height. Seasonal analysis shows that the increase in trend occurs mostly in mid-summer of the growing season, while the decrease in trend occurs in late spring. It is therefore suggested that the inter-annual variation and the long-term trend of the vertical CO 2 mixing ratio difference obtained from high-precision mixing ratio measurements on a tower in a forest could provide us with useful information on the carbon budget components.