The Bit Error Rate (BER) of Differential Chaos Shift Keying (DCSK) is analysed for both Single Input Single Output (SISO) and 2×2 Multiple Input Multiple Output (MIMO) configurations over multipath fading channels. Chaotic carriers are generated using a logistic map with control parameter r = 3.99 and spreading factor β = 128. Closed form BER expressions are derived for both architectures and cross validated through MATLAB simulations. In the SISO case, the derivation proceeds under Additive White Gaussian Noise (AWGN), while the MIMO model incorporates multipath fading and applies Equal Gain Combining (EGC) at the receiver to exploit spatial diversity. The 2×2 MIMO–EGC scheme reduces BER by approximately one order of magnitude relative to SISO at comparable SNR. Theoretical and simulation results agree well at low SNR; a divergence at high SNR is attributed to the Line of Sight assumption embedded in the analytical model, which sets the second-path coefficient to zero and therefore underestimates the diversity gain seen in simulation.