In this paper, the direction of arrival (DOA) estimation for noncircular sources in multiple-input multiple-output (MIMO) radar is dealt with by a novel nuclear norm minimization (NNM) framework. The proposed method exploits the noncircular property of signals to extend the data model for doubling the array aperture. Then a block sparse model of the extended data is formulated without the influence of the unknown noncircularity phase, and a novel signal reconstruction algorithm based on nuclear norm minimization is proposed to recover the block-sparse matrix. In addition, a weight matrix based on the reduced dimensional noncircular Capon (RD NC-Capon) spectrum is designed to reweight the nuclear norm minimization for enhancing the sparsity of solution. Finally, the DOA is estimated from the non-zero blocks of the reconstructed matrix. Due to exploiting the extended array aperture and block-sparse information, the proposed method provides superior DOA estimation performance and higher angular resolution. Furthermore, the proposed method has a low sensitivity to the priori information on the number of sources. Simulation results are presented to verify the effectiveness and advantages of the proposed method. HighlightsThe DOA estimation problem for noncircular sources in colocated MIMO radar is considered.A RD NC-Capon spectrum is formulation to design the weight matrix via solving a quadratic optimization problem.A reweighted nuclear norm minimization framework is proposed for DOA estimation.The proposed method provides superior DOA estimation performance and higher angular resolution due to exploiting the extended array aperture and block-sparse information.The proposed method has a low sensitivity to the priori information of the number of sources.