<p>Background: LHX1 is an important transcription factor for the <em>HDAC8</em> gene. The aim of this study was to investigate the effect of Sodium Butyrate (SB), as a histone deacetylase inhibitor, on the expression of <em>LHX1</em> gene in colorectal cancer cell lines.&nbsp;<br /> Methods: HT-29 and HCT-116 cell lines were treated with 6.25 to 200 <em>mM</em> concentrations of SB at 24, 48, and 72 <em>hr</em>. The cytotoxicity effect on cell viability was evaluated by MTT assay. The 50% Inhibiting Concentration (IC₅₀) was determined graphically. Quantitative real-time PCR was performed to investigate the LHX1 mRNA expression level.&nbsp;<br /> Results: Our study revealed that SB inhibited the proliferation of these cell lines in a concentration and time-dependent manner. The IC₅₀ values for HT-29 cell line were 65, 18.6, and 9.2 <em>mM</em> after 24, 48, and 72<em> hr</em> of treatment, respectively. The IC₅₀ values for HCT-116 cell line were 35.5, 9.6, and 10 <em>mM </em>after 24, 48, and 72 <em>hr </em>of treatment, respectively. Furthermore, real-time PCR findings demonstrated that the LHX1 mRNA expression in treated HT-29 cell line significantly increased in comparison with untreated cells (p&lt;0.05). However, in treated HCT-116 cell line, SB led to a significant decrease in the level of LHX1 mRNA (p&lt;0.05), as compared to untreated cells.&nbsp;<br /> Conclusion: In this study, different effects of SB on LHX1 mRNA expression level were revealed in two distinct human colorectal cancer cell lines.</p>