北方墨点法（英语：Northern blot）是分子生物学、生物化学中常用的实验方法，通过探测样品中的RNA（或隔离的mRNA）来研究基因表现。

利用探针侦测由凝胶电泳分离出来的RNA片段，寻找含有特定串行的RNA片段。与南方墨点法相似，RNA样品经过凝胶电泳后会按照大小分离，然后将样品从凝胶转印到膜上，并用与目标串行互补的标记的探针来探测。实验结果可以根据所用探针的不同以多种方式来观察，但大多数都显示的是样品中被探测的RNA条带的相对位置，也就是分子大小；而条带的强度则与样品中目标RNA的含量相关。这一方法可以测量目标RNA在不同样品中的情况，因此已经被普遍用于研究特定基因在生物体中表现的时刻和表现量，也是这类研究中最基本的手段。

The northern blot is a technique used in molecular biology research to study gene expression by detection of RNA (or isolated mRNA) in a sample.

With northern blotting it is possible to observe cellular control over structure and function by determining the particular gene expression rates during differentiation and morphogenesis, as well as in abnormal or diseased conditions. Northern blotting involves the use of electrophoresis to separate RNA samples by size, and detection with a hybridization probe complementary to part of or the entire target sequence. The term 'northern blot' actually refers specifically to the capillary transfer of RNA from the electrophoresis gel to the blotting membrane. However, the entire process is commonly referred to as northern blotting. The northern blot technique was developed in 1977 by James Alwine, David Kemp, and George Stark at Stanford University. Northern blotting takes its name from its similarity to the first blotting technique, the Southern blot, named for biologist Edwin Southern. The major difference is that RNA, rather than DNA, is analyzed in the northern blot.