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[Abstract] The authors present interference analysis toward the FS (Fixed Service) communication systems by the HEO (Highly Elliptical Orbit) satellite systems in Ka-band (17.7 – 19.2GHz). Especially, we treat two kind of HEO systems such as “Geosynchronous HEO” and “Sub-geosynchronous HEO” defined in ITU-R Recommendation S.1758. Geosynchronous HEO consists of 3 satellites of 24-hour period. Sub-geosynchronous HEO uses 3 satellites of 12-hour period. The authors provide the interference distribution maps and analyze the detail interfering conditions, by calculating I/N value on the assumption that each satellite system radiates interfering signals for 24 hours. The calculated I/N results are compared with the interference protection criteria determined by ITU-R Recommendation F.1495. Geosynchronous HEO satisfies the criteria perfectly because this is the regional communication system and transmit PFD toward the low elevation angle area is very small. On the other hand, Sub-geosynchronous HEO can not satisfy the long term protection criteria even if this system uses the modified PFD mask which is 8dB less than the RR mask in low elevation area. It is necessary to reduce I/N not only by suppressing PFD but also by using other methods.