The Sturm-Infanteriegeschutz 33B was a German self-propelled heavy infantry gun used during World War II.

After experimenting with open-topped mountings of the siG33 on the Panzer I and Panzer II, it was decided that a fully-enclosed compartment would be used for the next attempt. This new mounting utilized the hull as the Sturmgeschutz III Ausf E and F/8 but with a completely redesigned superstructure to create the StuIG33B. As with previous self-propelled vehicles mounting the siG33, production numbers were low, with only 24 having been completed from December 1941 to October of 1942 using Stug III Ausf E (12) and F/8's (12) chassis. The primary mission for these vehicles was knocking down buildings and other fortifications encountered during city fighting.

StuIG 33s were used exclusively on the Eastern Front. 12 of the StuIG 33s produced were used during the fighting in Stalingrad with Sturmgeschutz Abteilung 177 and 244, where they were all lost. The other 12 were used by Sturm-Infanteriegeschutz-Batterie Lehr Battalion XVII and then with 23rd Panzer Division.

The StuIG 33b mounted the improved (sIG 33/1) 150mm L/11.4 heavy infantry gun, offset to the right side; It could only traverse 3* left and right, elevate 25*, and depress 6*. An MG 34 machine-gun was fitted in a ball mount on the left side of the superstructure.