The purpose of this study is to investigate basic parameters which are essential for tidal correction of gravity data. This study involves computation of the theoretical values and laboratory measurements of tidal force of gravity. The theoretical variation of tidal force was computed according to the relative position of moon and sun on the celestial sphere by using a computer program Gravity measurements were carried out in Seoul University for 120 operation-hours, and also in coastal area in Incheon for 48 operation-hours. The gravimetric factor (δ) and phase delay were determined by comparing theoretical values with measured gravity data. Summarized results of this study are as follows ; (1) The gravimetric factor in Seoul is in the range of 1.22∼1.36(avg.=1.28) and the phase delay is in the range of 0.1∼0.3 hours (avg.=0.16 hours). (2) The mean garvimetric factor in Incheon is 1.31 and mean phase delay is 0.025 hours (3) The difference of mean gravimetric factor between in Seoul and in Incheon is 0.03 and that of phase delay is 8 minutes.