We present the results of the observations of molecular clouds in the Small Magellanic Cloud (SMC) with ALMA in the CO and [CI] lines. The SMC, with a metallicity of ~0.2 Zo, is one of the nearest galaxies and an important testbed for studying low-metallicity environments in distant galaxies. The molecular cloud properties have been studied mainly with CO and [CI] lines. Muraoka et al. (2017) found that CO lines behave as a somewhat dense tracer of ~10^4 cm^-3 and that the gas temperatures are estimated to be 40-60K. CO lines trace only about 10% of the total H_2 mass (Tokuda et al. 2021) when compared to the dust continuum observations with space telescopes. Thus, the CO lines in the SMC behave differently from typical galactic environments. However, the CO study revealed some common properties, such as the power-law exponent of the mass function (Ohno et al., submitted) and the ability to detect protostellar outflows (Tokuda et al. 2022). The [CI] line is expected to be more efficient at detecting H_2 gas in a low-metallicity environment, and indeed the [CI]/CO ratios are on average higher than typical galactic molecular clouds, but there are large spatial variations and no [CI] emission extends beyond the CO clouds (Onishi et al., in prep.). The behavior of CO and [CI] in a low metallicity environment is increasingly clear, and these studies can be extended to quantitative studies for star formation activity and interstellar matter in many galaxies with different metallicities.