Gravity and microearthquake surveys were carried out the Chinshan­ Tanshui area, northern Taiwan in 1987. Bouguer anomaly data w used to deter­ mine the subsurface structures of this area. The results indicate that the Chinshan fault is a thrust fault with a dipping angle of about 55 to 60 degrees. A temporary seismographic network with twelve stations w deployed to study the seismicity of the ea. 223 events with magnitudes between 0.2 and 3.2 occurred in the study area during the 58 days survey period. Most of them were at depths shallower than 10 km. om the fault plane solutions, we can see that most of the cal mechanisms in this area are from normal faulting. They must be co espond to the activity of the Tatun and Chishinshan volcanos. 433 earthquakes in the study area were recorded by the Taiwan Telemetered Seismographic Network (TTSN) during the period between 1973-1985. The distribution patte is quite similar to that re­ vealed by the temporary array. general, this area shows steady moderately active shallow seismicity.