They happened the evenings of Nov. 15 in the 5000 block of South Justine and Dec. 4 in the 5400 block of South Loomis, according to a community alert issued early Friday by Deering District police.
Both robberies were carried out by a group of four black men in their early 20s, with three wearing black hooded sweatshirts and one in white. One robber had dreadlocks, police said.
Anyone with information should call Area Central detectives at (312) 744-8382.