The seasonal variation of the earth's axial angular momentum budget is discussed with an error in the order of a few percent. The budget is based on the core-mantle decoupling (CMD) hypothesis, using the length of day (LOD) data observed astronomically by the International Radio Inteferometry Surveying and the atmospheric angular momentum data calculated from the forecast/analysis data set for numerical weather prediction of the Japan Meteorological Agency. The atmospheric relative angular momentum changes due to zonal wind account for an additional 23% contribution over the annual budget. However, this is counterbalanced by the effects of the redistributions of air and water masses. Namely, about 16% is accounted for by redistribution of air mass, and remained about 7% agrees with the contribution from surface wager storate estimate on condinents by Chao & O'Connor [1988>. These facts demonstrate a confirmation of the CMD hypothesis on time scale of a year. At the semi-annual period, however, there still is a shortage of about 6% in atmospheric and hydrospheric contributions of the budjet. ¿ American Geophysical Union 1990