In situ particle reinforced Al-4.5Cu/TiB₂ composite was fabricated with TiO₂, H₃BO₃, Na₃AlF₆ powders and Al-4.5Cu alloy by reaction in melt. The composite can be directly casted into moulds to make composite parts. TiB₂ particles distribute uniformly in the matrix. The average size of TiB₂ particles is 0.93 [ 0[`3]32 ]<sub>TiB2</sub> //[ 110 ]<sub>a- AI</sub> á 01[`1]1 ñ _TiB2 // á 002 ñ _{a- AI} and[ [`1][`3]2 ]_{a- AI} //[ 123 ]_{AI2 Cu} , á 211 ñ _{a- AI} // á 111 ñ _{AI2 Cu} \begin{gathered} \left[ {0\bar 332} \right]_{TiB_2 } //\left[ {110} \right]_{\alpha - AI} \left\langle {01\bar 11} \right\rangle _{TiB_2 } //\left\langle {002} \right\rangle _{\alpha - AI} and\left[ {\bar 1\bar 32} \right]_{\alpha - AI} //\left[ {123} \right]_{AI_2 Cu} , \hfill \\ \left\langle {211} \right\rangle _{\alpha - AI} //\left\langle {111} \right\rangle _{AI_2 Cu} \hfill \\ \end{gathered} . TiB₂ particle is nucleation site for -Al matrix growth in the composite. The interface between TiB₂ particles and the matrix is clean and well bonded. No reaction product has been found through HREM observation. This is beneficial to the strength of the composite. The as-cast Al-4.5Cu/TiB₂ composite exhibits mechanical excellent properties: the tensile strength is 416.7 MPa, the yield strength is 316.9 MPa, and the elongation is 3.3 pct.