¡@¡@Igneous activity of Taiwan in Miocene mainly were concentrated in the area north of Miaoli. Nanman is one of the basalt in southern of Taiwan that had been studied by OM, XRD, SEM/EDS and TEM. The rock type is alkali basalt with phenocryst of augite and olivine. The primary minerals include olivine + augite + plagioclase + Anorthoclase + apatite +titanomagnetite + illmenite, and secondary minerals are chlorite + smectite + calcite ¡Ó gypsum.Alteration of Nanman basalt was take placed in mixture and crack of olivine, other minerals are almost fresh. The main replacement are chloritic minerals shown five occurrence types : (1) replaced mixture, (2) vein center of olivine crack, (3) vien of olivine, (4) fibrous and (5) mica-like clay between vein and residual olivine. Each types has clear grain boundary. It¡¦s mean they are not gradual. (4) and (5) are smectite with anomaly composititon. It cause by lack of Al resource, and smectite occurred far from the crack that element do not easily move. Thus, smectite replaced olivine often showed Al-poor and excess Mg. Si/(Si+Al) and Fe/(Fe+Mg) in smectite is positive correlation. This may be considered the moving ability of elements. Composition of (1), (2) and (3) are chlorite/smectite. However there is no observed mixed-layer minerals in XRD. According to TEM , they are chlorite + smectite. Chlorite within abundant of dehydrated cracks could be a evidence of smectite. Because of mixed chlorite and smectite, the correlation between Si/(Si+Al) and Fe/(Fe+Mg) is negative. Different occurrences lead to different mineral, suggest water/rock ratio is an important control factor. High rock/water ratio trend to form chlorite, and low rock/water ratio prefer to form smectite. According to all the results, the steps of altered olivine are first forming chlorite at mixture and olivine cracks. Then, the residual olivine becomes smectite with poor Al and excess Mg, when the rock was cooling down.