This invention relates to a helical intake port for an internal combustion engine comprising a straight passage, a swirl passage connected to the straight passage and formed in a spiral around the center of an intake valve, and a cylindrical throat connected to the swirl passage via an opening over the whole area of the swirl passage. The cross-sectional area S of the swirl passage is determined by the following equation: ##EQU1## where: .beta.=swirl angle from swirl start position,.beta.0=whole swirl angle from swirl start position to swirl end position of swirl passage,S0=cross-sectional area of swirl passage at swirl start position.As a result, swirl can be enhanced and a high flow coefficient of the intake port can be realized.