Well-defined tubular inclusions were detected in mesophyll chloroplasts of young Sedum rotundifolium leaves. The size and distinctly uniform arrangement of tubular inclusion were the most noticeable features. The chloroplast usually contained a large inclusion, sometimes extending almost as long as the chloroplast. Such inclusions were built up from microtubules exhibiting aggregates of either large plate-like or paracrystalline structures depending on the section angles. These inducsions wre often quite huge, measuring as much as 7.1${mu}{ extrm}{m}$ in length and 2.6${mu}{ extrm}{m}$ in width. The diameter of the microtuble was aproximately 25 nm. The microtubule aggregates were no-nmembrane bounded structures endlosed partly by the thylakoids. The microtubules in the aggregate were all displaying the same definite orientation. Cross-sectional views clearly demonstrated the characteristic hexagonal arrangement within paracrystalline structures. Longitudinal sections of the chloroplast microtubules showed that they were in perpendicular orientation to the chloroplast envelope. They were not connected to these membranes in any case. In general, one microtubular aggregate was seen in each chloroplast section. The role of tubular inclusions in the chloroplasts related to the photosynthetic mode was discussed.