Moscoso, 28, pitched for the Colorado Rockies last season. He was 3-2 with a 6.12 ERA in 23 appearances including three starts. He started 21 games with Oakland in 2011 with an 8-10 record.
Moscoso will battle lefty Hisanori Takahashi and righty Cory Wade for the final bullpen spot. Moscoso could fill the void left by Carlos Villanueva, who was promoted to starter this spring. With Villanueva in the rotation, the Cubs don't have true long reliever on the roster.
The Cubs also placed pitcher Arodys Vizcaino on the 60-day disabled list to make room on their 40-man roster. The Cubs likely will have to make one more move before the regular season to accommodate the addition of the final reliever and non-roster invitee Brent Lillibridge.