Air-atomization　technique　was　used　to　produce　microcapsules　filled　with　carbon　dioxide,　which　have　the　potential　to　become　ultrasound　contrast　agents,　and　the　factors　affecting　the　size　of　the　microcapsules　were　studied.　An　alginate-containing　mixture　gel　was　sprayed　to　a　calcium　salt　solution,　usually　calcium　chiloride.　Carbon　dioxide　containing　microcapsules　with　mean　size　around　5μm　were　made.　Experiments　were　conducted　to　investigate　the　effects　of　the　alginate　concentration,　the　air　pressure,　and　the　syringe　pump　rate　on　the　size　of　produced　alginate　microcapsules.　Furthermore,　the　influence　of　the　distance　from　the　syringe　tip　to　the　surface　of　the　hardening　solution　on　the　shape　of　alginate　beads　was　studied.