Search for heavy Majorana neutrino in lepton number violating decays of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>D</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>K</mml:mi><mml:mi>π</mml:mi><mml:msup><mml:mi>e</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:msup><mml:mi>e</mml:mi><mml:mo>+</mml:mo></mml:msup></mml:math>

Using a data sample with an integrated luminosity of $2.93\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ taken at the center-of-mass energy of 3.773 GeV, we search for the Majorana neutrino (${\ensuremath{\nu}}_{m}$) in the lepton number violating decays $D\ensuremath{\rightarrow}K\ensuremath{\pi}{e}^{+}{e}^{+}$. No significant signal is observed, and the upper limits on the branching fraction at the 90% confidence level are set to be $\mathcal{B}({D}^{0}\ensuremath{\rightarrow}{K}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}{e}^{+})&lt;2.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$, $\mathcal{B}({D}^{+}\ensuremath{\rightarrow}{K}_{S}^{0}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}{e}^{+})&lt;3.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ and $\mathcal{B}({D}^{+}\ensuremath{\rightarrow}{K}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}{e}^{+}{e}^{+})&lt;\phantom{\rule{0ex}{0ex}}8.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. The Majorana neutrino is searched for with different mass assumptions ranging from 0.25 to $1.0\text{ }\text{ }\mathrm{GeV}/{c}^{2}$ in the decays ${D}^{0}\ensuremath{\rightarrow}{K}^{\ensuremath{-}}{e}^{+}{\ensuremath{\nu}}_{m},{\ensuremath{\nu}}_{m}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}$ and ${D}^{+}\ensuremath{\rightarrow}{K}_{S}^{0}{e}^{+}{\ensuremath{\nu}}_{m},{\ensuremath{\nu}}_{m}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}$, and the upper limits on the branching fraction at the 90% confidence level are at the level of ${10}^{\ensuremath{-}7}\ensuremath{\sim}{10}^{\ensuremath{-}6}$, depending on the mass of the Majorana neutrino. The constraints on the mixing matrix element $|{V}_{e{\ensuremath{\nu}}_{m}}{|}^{2}$ are also evaluated.