The 20-year-old New Zealand striker has agreed a switch to The Den until November 20, although Albion can recall him after the first 28 days.
Wood, who scored a hat-trick against Millwall while on loan at Birmingham last season, is available for Tuesday night's visit of Cardiff.
He told the Lions' official website: "I'm not in the first-team picture at West Brom so I'm dying to start playing regular football again.
"In January I will give some thought to my longer-term future, but for now I'm just looking forward to playing for Millwall and hopefully scoring some goals."
Source: PA
Source: PA