This paper proposes a modified interleaving resonant switched capacitor converter with reduced output resistance and in-situ startup. The operation principle, especially the average output voltage, the average flying capacitor voltages and the output resistance are theoretically deduced. The proposed converter reduces the output resistance by using fewer switches in some current paths. Besides, the proposed converter takes an in-situ flying capacitor pre-charge scheme to guarantee a safe startup. Here, we simulate both the conventional and the proposed converters in Cadence Spectre with the commercial device models. The proposed converter improves the heavy-load efficiency from 92.7% to 93.2% with VIN = 48 V and VOUT = 12 V, leading to around 7% total loss reduction.