Abstract: A portable grinder may include a side cover having inner threads and a cover receiving space, said inner threads used to engage with middle inner threads of a middle piece; a first grinding piece, one side of which having a plurality of first grinding protrusions and a plurality of through holes scattered at various locations between the first grinding protrusions; and the other side having a screening unit; a middle piece adapted to receive the first grinding piece and connect to a second grinding piece through a bearing; and a second grinding piece having a plurality of second grinding protrusions facing the first grinding protrusions, wherein substances to be grinded are disposed in a second receiving space between first and second grinding protrusions, and the first and second grinding protrusions of the portable grinder are driven by gravity to spin to grind the substances therein.