Effect of different physiological states of cultured bighead carp before deathon its post-mortem changes of ATP and its related compounds in the duration of rigor mortiswas studied in this paper in association with its change of freshness measured by K valueduring this period. The results were summarized as follows:(1)The time from death to full rigor (Tr) was directly dependent on the initial contentof ATP and lactic acid (la) after death. The degree of depletion of ATP and glycogen beforedeath was the decisive factor for the Tr, so it is important for the improvement of freshnesskeeping technique.(2)Along with the fish muscle reached full-rigor state, the IMP concentration (IMP)increased to the highest level, then decreased slowly, and kept at a higher level before theresolution of rigor mortis beginning. On the other hand, K value ascended accompanyingwith HxR and Hx accumulation.(3) For bighead, silver carp and grass carp in different seasons, when the musclereached full-rigor state, the K value was less than 20% which means high freshness of fish.But when it reached rigor-resolution, the K value that showed a degradation of freshness offish might be kept within 20% only in the spring or summer season, when the time reachingrigor-resolution was much shorter. As in autumn or winter, the K value would be more than20% even 40% when the time reaching rigor-resolution became longer.