The study was attempted to examine the health-condition of Taiwan red cypress (Chamaecyparis formosensis) and acid rain issue with the species over Yi-Lan area in northeastern Taiwan by using multi-stage, multi-date remotely sensed images. This study performed the following steps: (1) to collect data and build a GIS database; (2) to correct four-date SPOT images using relative radiometric normalization; (3) to produce the normalized difference vegetation index (NDVI); (4) to perform change detection on four-date NDVI images; (5) to compare the map of health-condition deteriorating Taiwan red cypresses (TRC) with acidic intensity map of acid rain; (6) to confirm the comparison results by high resolution ortho-rectified images. Results indicated that the overall health-condition of TRC in Yi-Lan area had a small ameliorating tendency based upon change detection of four-date NDVI images. Based upon pixel-by-pixel image analysis, the area of health-condition ameliorating TRC was about 2.3 times as many as that of health-condition deteriorating TRC in Yi-Lan area. More importantly, the acidic intensity distribution of acid rain over Taiwan, having a descendent tendency from northwest to southeast direction, did not agree with the distribution of TRC health condition, the area of health-condition deteriorating TRC in the northwestern portion of Yi-Lan fewer than that in the southeastern portion. Therefore, acid rain was not a key factor causing deterioration of the part of TRC in Yi-Lan area; however, the possibility of its detriment to TRC cannot be fully eliminated at present. Intensive land exploitation in Yi-Lan area was found to be the highest potential factor via confirmation with high-resolution ortho-rectified photos. Anthropogenic detriment to TRC in Lan-Yan area significantly exceeded that of acid rain, thereby probably disguising the subtle effect of acid rain. Long-term monitoring acid rain on the ground and by remote sensing should be continued.