膜间隙（英语：intermembrane space，简称IMS）是指线粒体或叶绿体的内膜与外膜之间的区域。膜间隙的主要功能是进行氧化磷酸化。

位于外膜的叫做孔蛋白的一类信道蛋白允许离子与小分子自由移动进入膜间隙。这对于与这些细胞器功能相关的溶质来说，并不意味着他们与胞质溶胶之间在本质上是连续的。驶往线粒体基质或组织基质的酶可以以运输的方式穿过线粒体膜间隙。线粒体中的移位酶有的在线粒体外膜上（TOM）有的在线粒体内膜上（TIM，叶绿体中的移位酶有的在外膜上（TOC）有的在内膜上（TIC）。在电子传递期间，因为质子梯度的缘故，膜间隙倾向于低pH，当质子从线粒体基质被泵入膜间隙时就会产生质子梯度。负责形成质子梯度的相应细胞结构包括了：辅酶Q、NADH-辅酶Q氧化还原酶复合体（复合体I）、琥珀酸盐-辅酶Q氧化还原酶复合体（复合体II）与辅酶Q-细胞色素c氧化还原酶复合体（复合体III）。

The intermembrane space (IMS) is the region between the inner membrane and the outer membrane of a mitochondrion or a chloroplast. The main function of mitochondrial intermembrane space is oxidative phosphorylation.

Channel proteins called porins in the outer membrane allow free movement of ions and small molecules into the intermembrane space. This does not mean that it is essentially continuous with the cytosol in terms of the solutes relevant for the functioning of these organelles. Enzymes destined for the mitochondrial matrix or the stroma can pass through the intermembrane space via transport through [1]s. These are known as translocase of the outer mitochondria membrane (TOM) and translocase of the inner mitochondrial membrane (TIM) in mitochondria and translocase of the outer chloroplast membrane (TOC) and translocase of the inner chloroplast membrane (TIC) in chloroplasts. It tends to have a low pH because of the proton gradient which results when protons are pumped from the mitochondrial matrix into the intermembrane space during electron transport. The structures responsible for this are coenzyme Q, NADH coenzyme Q oxidoreductase complex (complex I), succinate-coenzyme Q oxidoreductase complex (complex II), and coenzyme Q-cytochrome c oxidoreductase complex (complex III).