There is provided a downsized electrical connection box in which the reliability of the mechanical connection between blocks provided in the electrical connection box is improved. The electrical connection box 1 includes a plurality of electric components, a first block 3 mounted with the electric components and a second block mounted with the electric components. The first block 3 includes a tubular-shaped first member 32, 33 projecting towards the second block 5. The second block 5 includes a second member 52, 53 arranged to be slidably inserted into the first member. The first and the second blocks 3, 5 are coupled to each other by slidably inserting the second member 52, 53 into the first member 32, 33. At least one electric component 8 of the plurality of electric components is received inside the first and the second members 32, 52, 33, 53.