A laboratory study revealed the dynamic changes of solids in swine manure during storage in order to determine the best time for efficient solid-liquid separation treatment. Data showed that separation should be conducted within 10 days after manure excretion for particle sizes equal to or greater than 0.5 mm and within five days for particle sizes smaller than 0.5 mm. After the first 10 days of storage, the total suspended solids tended to be decomposed at a higher rate, thus reducing separation efficiency. Particles equal to or smaller than 0.25 mm were biologically decomposed at the same rate without relevance to the particle size during the first 20 days of storage. The level of total volatile solids in liquid manure was linearly correlated with the total solids content with a correlation coefficient of 0.9850 in the 30-day period.