The joint-stiffened honeycombs have attracted increasing interest recently due to the improved stiffness, strength and energy absorption properties. Undoubtedly, stiffened joints play a significant role in the equivalent in-plane elastic moduli (EIEM). This paper proposes an analytical homogenization for EIEM of honeycomb with stiffened joints (HSJ). First, the stiffness matrix of a honeycomb cell wall (based on rod and Timoshenko theories) connected to stiffened joints (modelled as rigid bodies) is formulated. Based on the unit cell method, closed-form expressions of EIEM are proposed, which are sufficiently general to be applied to three types of honeycombs. The closed-form expressions are validated very well by numerical simulation and experiment. Furthermore, the proposed expressions are applied to hexagonal, auxetic and square HSJ and the dependency of EIEM on inclined and vertical sizes of stiffened joints is discussed. The results show that Young’s moduli and Poisson’s ratio are strongly related to the size of the inclined section of stiffened joints; while shear modulus is strongly related to the size of the vertical section. It is also found that the improvement of Young’s modulus for aluminium joint-stiffened nylon honeycomb can reach up to 41% compared to nylon honeycomb under the same weight.