After first' report of rli.s^oveiin} pseudomorphous oetahedra of serpentine in 1981 pseudomor-phous octahedra of chrom-barring chlorite also has been diseovered in chromite of the same ultra-mafic rocks.Chlorite is the substitution product of serpentine.Basad on reseaeh rosults we can make following conautionse 1. the piim}ry mineral of oetahedral pseudomorphous chlorite must be γ-olivine. The pressure of formation of γ-olivine was about 140kb, corresponds to 500km in depth;2. Al, Cr of pseudomorphous ocLrherlra must come from chiomite} 3. Chromite including pseudomo-rphous octahedra of serpentine and chlorite, may be a type of directly coming from lower part. of mantle; 4. North Tibet ultramafic rock belt would be formed deeper than that in South Tibet belt, because pseudomoiphous octahedra are found only in North Tibet ultramafic rock belt.