  In this paper, we show that $W^{1,p}$ $(1\leq p<\infty)$ weak solutions to
divergence form elliptic systems are Lipschitz and piecewise $C^{1}$ provided
that the leading coefficients and data are of piecewise Dini mean oscillation,
the lower order coefficients are bounded, and interfacial boundaries are
$C^{1,\text{Dini}}$. This extends a result of Li and Nirenberg (\textit{Comm.
Pure Appl. Math.} \textbf{56} (2003), 892-925). Moreover, under a stronger
assumption on the piecewise $L^{1}$-mean oscillation of the leading
coefficients, we derive a global weak type-(1,1) estimate with respect to
$A_{1}$ Muckenhoupt weights for the elliptic systems without lower order terms.
