In this study lightweight cement mortar was researched. Low-density mortar is used for cementing high temperature, heavily watered oil and gas wells. ISO standard methods, X-ray diffraction analysis and electron microscopy confirm that hollow microspheres of perlite are an effective lightening component for cementing slurry. The results show that admixing microspheres reduces slurry density to 1400 kg/m3. Cement stone with the 3% perlite microspheres has an increased strength of 1.9 MPa due to actual interaction of the cement matrix with the aluminosilicate substance of microspheres, the self-reinforcement of the cement matrix by use of ettringite crystals. Cellular multi-chamber structure of perlite microspheres with the reactive surface enhances water-retention of cementing slurry. Use of the perlite microspheres as a facilitating additive for grouting slurry is preferable in comparison with glass microspheres. Low-density cement mortar with perlite microspheres is recommended a lightweight solution for cementing oil and gas wells.