The synthesis of a new series of 1$eta$-methylcarbapenems having 5-($alpha,eta$-disubstituted ethyl)pyrrolidine moiety is described. Their in vitro antibacterial activities against both Gram-positive and Gram-negative bacteria were tested and the effect of substituents on the pyrrolidine ring was investigated. A particular compound (VIh) having $alpha$-hydroxy-$eta$-piperazinylethyl substituted moiety showed the most potent activity.