In this study, we investigated the variation in free sugars, amino acids, antioxidant activity, and anti-inflammatory activity of Solanum nigrum Linne based on harvest time. Major amino acids identified by HPLC analysis were proline, histidine, and serine. The highest content of total amino acids were found in S. nigrum aerial parts and roots harvested on July 10th and August 10th. Four kinds of free sugars (fructose, glucose, sucrose, maltose) were detected in S. nigrum, and the free sugar content varied significantly with harvest time. The fructose content of S. nigrum decreased with as harvest time increased. The total polyphenol content of S. nigrum was highest in those harvested on August 30th. The antioxidant activity of ethanol extract from S. nigrum collected at different harvest times were measured by DPPH and ABTS radical scavenging assays. The anti-inflammatory activity of these extracts were assayed via nitric oxide suppression in C6 glioma cells with a lipopolysaccharide (LPS)-induced inflammatory response. The anti-inflammatory activity and antioxidant effects were the highest in the extract from S. nigrum collected on August 30th. Good correlations were observed between antioxidant and anti-inflammatory activities in ethanol extract of S. nigrum roots harvested on August 30th.