Abstract: The cell strain ZC-7901 of Grass Carp snout tissue was adopted for the research of packing from basic chromatin fibres to chromosomes.In studying of the subject,four methods were used:The induction of premature chromosome condensation in interphase nuclei by fusing with metaphase cell;the "elongation" of chromosomes; the moderate hypo-osmosis of culture cells and spreading chromatin.Scanning and transmission electron microscopes were used to investigate the prepared specimens.The observations showed that the basic structure of fish chromatin was the same as that of mammalians,which was the nucleofilament of 10 nm in diameter.There were two patterns from the chromatin packing into the chromosome:One was the multiple spiralization from the basic fibre into the chromatid of about 300 nm in diameter,and then to the sister chromatids which twisted into the chromosome;the other one was the directly fold coupling from 30 nm or 60 nm solenoids into the chromosome in which the partial helical irregular fibres coexisted.It was suggested that the spiralization was the normal packing pattern of the chromosomes of Grass Carp,and the fold coupling was the rapid and premature condensation.